I'm approaching 30 and it feels utterly bizarre. When I was a kid I thought at a certain point (presumably in your 20's) you'd feel like an adult, that it would follow looking and acting like one I guess. But I don't feel that's happened. Like, I feel as though my growth has been stunted, even though it hasn't. I own my own house, rent out properties, have a responsible job, travel, been intimate with dozens of different women, etc. All the other mundane adult things, bar getting married and having kids which a) I'm not sure is something I ever want and b) feel utterly unprepared for for the aforementioned reasons. Despite all this, and living a fairly successful adult life I still feel essentially identical to the first summer after I left school, was unemployed and living with my parents.
On the upside, I still manage to pass for 19-21 or so, and people are regularly shocked to find out I'm 28 (29 in a couple months) which is alright I guess.