They did that for Gen Z, where it’s essentially the dividing line between people who were more or less cognizant when 9/11 happened, and those who weren’t.
I didn’t come up with the age range, but it’s been well established for a while now. Someone else told me about “Generation Jones”, which is basically just the younger half of the Boomer generation I guess. I feel like that’s splitting hairs, but who knows, maybe it makes some sort of sense to you?