According to this paper, which I have no idea what it says, the Earth may be about 12.5 billion years old. This is younger than the previously favored answer, which put the universe at 13.8 billion years old.
More precisely, or actually, less precisely, the lead author on that paper says that the universe may be between 12.5 and 13 billion years old.
So, that hold-the-date card they sent out for the 14 billion year anniversary of the universe? Keep it tacked to the fridge for now, but be prepared to pencil in a new date.