There's always something. I find I have some issues because I'm 44 but everyone at work seems to think I am between 35 and 40. I think it gets my behavior misinterpreted. And I have had people say horribly insensitive things in front of me about how forty is just around the corner for them and "how scary is that?!" and similar. (Someone who knew my age, which is why I feel it is insensitive. And it was a pattern of behavior over a period of months, not a stray remark. Still, I suspect this person just doesn't really think of me as "over 40", even though they know I am, and I think that is part of why they blathered on thoughtlessly in front of me about their negative feelings about their own age.)
I'm still trying to figure out what causes people to perceive me as younger than I am. I find it baffling. But it has happened on the Internet too. So I suspect it is in part behavior-related, not just a looks thing.