Measuring a Generation-A World Population
It should be kept in mind that because WWI was a world event, the entire world population can be used to take the measurement of a generation. WWI was declared, erupting on July 28, 1914 a historically marked time period. Therefore, anyone born on and before July 27, 1914 is part of the pre-WWI generation. Most were also alive to experience WWI at that time. (If a person wants to be accurate to the extreme, you can use the very day, hour, minute and second before WWI was declared to divide the pre-WWI generation from the WWI generation. Just find the official document of declaration of war and check for a time stamp, if one exists.)
Statistical Data
It is possible to know how many people are still alive from that WWI area. According to the World Almanac there were approx. 1.6 billion people on the face of the earth about that time. As always the world population age ranged from the very oldest people to the newest born babes. Today in 2017 those newest born babes are some of the oldest people on the face of the earth
In 2014 it was estimated by the United States that there were 450,549 (1)(5) people around the world who were 100 years old or older. Statistically, of all those who live to be 100 years old, only 1 out of 1,000 will live to be 110. That means at the 110 year mark from the date of July 27, 1914, there will be at best approximately 451 people round the world who will be 110 years old and older.
According to supercentenarian studies, (supercentenarians are people 110 years old and older)(3) once people hit the age of 110 they will die off at 2 out of every 3, until full mortality is reached at around 114 to 116 years of age, with possibly, not always, only a very few, 1 or 2 or so, going beyond that age. Very few make it to 117 or older. In fact from 1955 to the time of this writing, March 2017, only six verifiable people have lived to be 117. Only 2 lived beyond that age, one to 119 and the other, Jeanne Louise Calment who lived to 122 years, 164 days. Most of the oldest living people died at 114 years of age. (Keep in mind researchers are unable to determine whether they have all the information at hand and so use best figures at that particular time.)
The question is how long will they live and so mark the end of the Pre-World War One generation? Only time will tell. (One point of note: the Spanish Influenza took many lives and may have cut short the length of time of the oldest living people from that pre-WWI generation, the WWI generation and the post-WWI generation. Nevertheless as always, when the last one dies, regardless of their age, the generation dies.)
The WWI Generation
WWI ended on November 11, 1918. Therefore the generation of WWI was composed of those people living when WWI broke out and those who were born during WWI. (July 28, 1914 to November 10, 1918.) Once the last pre-WWI generation member dies, the next generation to become the oldest living people on the face of the earth will be those who were born during WWI. They will die off a few years after the pre-WWI generation. Anyone born after Nov.10, 1918, is not of the WWI generation but they are part of the post-WWI generation.
This being said, people live through various events in their lives. Someone who was part of the pre-WWI generation, if they lived long enough, was also part of the WWI generation and the post-WWI generation. If they lived even longer they were also part of the pre-WWII generation and the WWII generation. Some of them actually participated in WWII. (Note: the post-WWI generation can also be known as the pre-WII generation depending on how someone wants to present an idea.)
A Step Down
A generation can also be used to mean a step down or the next step in the line of one’s decent. As an example, a married couple who were born in the pre-WWI era has a baby born the day after WWI began. That baby cannot be part of the pre-WWI generation. But it is a part of the WWI generation as are the parents. Generations cannot perpetuate but events can go on a long time after a generation has died such as some wars which have historically lasted hundreds of years.
Consider the seasons of the year. Summer, fall, winter and spring are specific. They each are definite marked time periods starting on a given day every year and ending on a given day every year. Spring does not and cannot perpetuate or overlap into summer regardless of the temperature or world events. So it is with a generation, it is marked either by a specific historical date or calendar year. When the last oldest living person dies, the generation dies. Generations come and go just as spring time and the other seasons come and go. Multiple events can go on within the life of a generation. Likewise the reverse is true, past wars of history have prolonged for hundreds of years, while multiple generations have been born and died within those war years.
There may be some claims that generations are built around historical events. However, this claim brings up the question, when does the generation end? How many years after an historical event must be counted to still mean a specific generation is in existence? It becomes arguable and hazy and not worth discussing as it yields no certain answer. It is much more specific and exact to count those who were born after an event ended as the post- generation of such an event.
Use of the Word Generation
BEWARE: It’s important to know how the word generation is being used within the context of the speaker or writer to understand the specific meaning of the word. This report doesn’t cover every use of the word. See a dictionary for more information.
Unverifiable Ages
At this point take note we have been dealing with verifiable birth records and not unverifiable claims of a person claiming to be older than those whose ages are verifiable. How these unverifiable individuals should be viewed depends upon other factors or questions. Here are some examination questions to use to determine if such a person’s age can be accepted. (4)
1) Is the person male or female? Usually women live longer than men. So the odds against male claimants being the age claimed is reduced but not out of the question.
2) Is the person from a developed country or a third world country? In third world countries there is usually little to no health care and more lawlessness. A person’s life is cut short by these and other factors.
3) Is the person literate? If the person is not literate, they probably can’t count. Nonetheless to be certain, ask the person if they can count? If so, ask when did they learn how to count? Was it late in life? If late in life this isn’t a valid test. But if a person claims they learned to count at an early age, use this test:
As an example, if a person claims to be 150 years old, ask the person to count from 0 to 150. If that person misses half the numbers than its probable that person is 75 years old or close to that age. In other words, however many numbers they miss during the count, subtract that from the age they claim.
4) Does the claimant know what a calendar is? Do they know how to use it? If they never or sporadically had a calendar, then it’s much easier to lose track of time and they may have guessed at their age now and then.
5) Does the person smoke, chew tobacco, use drugs for recreation, over eat or engage in any habits that cut a person’s life short? In developed countries these habits, despite medical care, do indeed cut one’s life short; so it becomes very questionable if a third world claimant is the age they claim.
6) Does the person have any health problems? As an example, a weak heart. This in itself will affect a person’s memory as a weak heart doesn’t pump enough blood to the brain and so affects the memory.
In conclusion, anyone who can’t verify their claims to be older than those who can validate their age is probably not accurate and should be held highly questionable and probably discounted.

References:
(1) World Population by Age and Sex – U.S. Census Bureau
https://www.census.gov › … › Data › International Data Base

(2) List of the verified oldest people – Wikipedia
https://en.wikipedia.org/wiki/List_of_the_verified_oldest_people

(3) Supercentenarian – Wikipedia
https://en.wikipedia.org/wiki/Supercentenarian

(4) Typologies of Extreme Longevity Myths – Hindawi
https://www.hindawi.com/journals/cggr/2010/423087/
(5) (http://www.un.org/en/development/desa/population/theme/ageing/index.shtml). Their current estimate for world population 100+ in the year 2015 is 451000
See Also:
Centenarian – Wikipedia
https://en.wikipedia.org/wiki/Centenarian

Guinness World Records, see oldest living person.
(https://esa.un.org/unpd/popdev/Profilesofageing2015/index.html). If you have further questions on this information, you can contact Population Division directly at population@un.org.
“Table C – World’s Oldest Person (WOP) Titleholders Since 1955”. grg.org. Retrieved 27 July 2015.

We know how long people in North Africa, the Middle East, and West Asia lived during the Neolithic, Bronze Age, and Iron Age (thus, covering even the broadest possible interpretations of the bible in time and space.

They had pretty average, typical lifespans for humans. Nothing extraordinary.

We know this because we have their bodies.

The only way we could be wrong about this is if some very basic physics and cellular biology was totally 100% wrong. It isn’t. So, we know.

The interesting challenge, then, is to understand why the bible gives some of the patriarchs such great age. There have been many theories, and in my view, they are all flawed by one single thing: They assume that a single adjustment or explanation applies generally across a range of texts. That is pretty absurd given the nature of the texts.

Humans do certain things (and make certain mistakes) that we know a fair amount about, and that provide plenty of room for explanation. Epochs. Patrilines. Mytyical ancient patriarchs. Math error. Ming up the words like “Mwezi” and “Mwanza” … that’s an example of year and month in a particular language as an example of how easy that might be to get wrong.

We know for certain that these biblical lifespans of 900 years, etc. are wrong. There is no question about that. That is not a matter of opinion.

Meanwhile we know that the bible is not an historically accurate document in any time frame. No collection of ancient documents that conflates, in its modern form, three separate origin myths can possibly be. You can’t build an absolute time line from the bible, for the most part.

First of all, I realized that we tend to measure everything in the present as though all life as it occurs today was always the same having the same life spans we witness today. This is, of course, the uniformitarian idea assumed under the evolution paradigm.

However, if one accepts the bible as a source of history, life spans differed quite markedly from those of the present. (And I am well aware that many people do not accept the bible as a true reflection of history which is a debatable point.) Many of the earliest ages reported in the bible were remarkably long and began to change markedly after the great flood.

Although, many people are skeptical of these time frames, I believe they could, in fact, be more valid than we have been led to believe. That is, longer life spans would make sense for a couple of reasons. They would also have an impact on generational calculations.

First of all, geneticists are noting that human beings have accumulated quite a few mutations over time (about 10 per generation are retained in the code according to the geneticist author of Genetic Entropy John Sanford.) These accumulations over time are reaching a point whereby they are having a direct impact on human health and quite possibly shortening our life span as well.

Additionally, during the early stages of human life on the planet, the code was cleaner (along with the food/water supply and natural conditions) with fewer mutations which would in turn also contribute to longer life spans.

A major catastrophic change like the global flood reported in Genesis would have had an impact on life spans due to the major transformations of natural living conditions on the planet after the flood. In fact, making the planet less hospitable particularly in the early centuries after the catastrophe with major climatic changes etc.

Biblically, life spans reported in the bible begin shortening to levels similar to those found today in the generations after the flood which would support those assumptions.

At any rate, the generation measurement level of 25 years, while accurate for todays time frames, would probably not be an accurate measure when stretched over the entire reported history of human kind.

So my idea to use the time measurements based on the accepted generational differences of modern day would probably not work when applied to the whole time span as reported in the bible because when people lived longer, they also married later and had children at much later ages as well.

Hence, with the realities of less mutations in the genetic code and changes in natural living conditions due to catastrophe, I realized that I would not be able to effectively correlate generations reported biblically with the age of human kind. Now, I wonder if anyone actually has accurately done that accommodating the life span changes mentioned above into their calculations?