I’m still in my 20s, but as of a few years ago I started forgetting what’s my exact age. I always have to stop and recalculate it each time someone asks me. I get asked fairly infrequently, but when I do it’s a bit weird/embarrassing that I have to say “wait, let me calculate”. (I know when I was born, of course.)
It seems as if there’s no good reason I’d remember it, since it changes all the time and it is rarely mentioned in practice. But others, including people much older than myself, know their own age immediately.
I’m also terrible at remembering people’s names, I don’t know if that could be related?
A few months ago I was doing dishes and for some reason thought about my age and I literally couldn’t remember if I’d hit 50 yet. Had to do the math to remember I’m 45 and that’s quite a ways off. That’s an outlier for sure, but yeah I forget.
It just doesn’t come up often. There are fewer ands fewer markers. Before your 20s you’ve got hitting double digits, becoming a teenager, sweet 16, becoming an “adult”, then not being a teenager any more. In your 20s you’ve got becoming an adult again (and maybe being able to drink if 21 is your drinking age), and then maybe saving money on insurance at 25 if that even matters to you. Then nothing. You might demarcate 30, but nothing really changes. In many senses now it’s “just a number” and the individual increments fail to matter. There’s no differential reinforcement to remembering where you are on the number line.