Comment by icegreentea2

I agree with your observation, but at the same time, I do think that what a lot of these people might be expressing is their observation of the disconnect between their socially implanted expectations (you're an adult when your 18/21! you are now -mature-), and their experience reality. Which is that for many (most?) people who go through the typical North American education pipeline through university/college (and I'm only making this limitation because that's my experience, and the experience of most of my friends), that looking back, they were definitely not "mature" at 18/21. They probably weren't even mature when they graduated undergrad or started their first full time job out of school.

Everyone has a different point, but they typically recognize somewhere in their 20s that 'oh wow, we keep changing and maturing'. And the first, most basic way to express this observation is with a pretty crude 'oh wow I'm old'. I think eventually, most people can move beyond that first reflexive observation.