I agree, but I think I understand why I do it.
TL:DR Maladaptive behavior that is however ultimately harmless since I don’t bother people.
I was a “gifted child”; was always like 2 school years ahead, started uni at 15 and every single person I met would praise me for being the youngest. I was immature so it got to my head. I also have always looked much younger than I am, which also invites comments. Finally, I also have AuDHD and I’m constantly anxious about not acting my age and being too immature. So I try to look at other people’s ages to guide me in how I’m supposed to behave.
All of this is maladaptive and I’ve gotten a lot better with time, and I’m still working on it, but I’m not particularly bothered about the actual fact of having an interest in people’s ages. I make sure I don’t ask them about it or bother them about it, but many just offer this information on their own.
Can confirm. This is my entire life.