Oh yeah, I feel a lot like that especially in areas of life I didn't have the chance to behave like a kid. Younger I've always felt older than I am and now there are moments I feel like I regress and don't get to understand stuff of my age. I see friends getting into the jobs and housing and kids and family things and it all looks so alien to me, I'm getting in my 30ies and honest what looks like a desirable life now is to go out and take drugs. I didn't get to get chaotic. Now I'm not gonna do it unsafely but it's kind of a sadness I have I didn't enjoy myself at all for most of my youth.
So now, I do actual kids stuff. Playing in carousels, playing games, cracking silly jokes, running and jumping and giggling. Eating marshmallows lol.
I'm lucky I'm in a domain where it's possible (I'm studying video games development) and where that kind of playful behaviour is not only considered normal but positive. Before that I was in contemporary art (still am a little though) and the seriousness of it really ended up eroding me. There is a reality to the cliche of people dressed in black and birching about one another.
All this to say I think that feeling set back really has to do with the frustration of not having had the experiences that we would have wished to have, like we spent time in a parallel universe with no access to the main reality of most of people. Which in a sense is true. Dissociation made me spend countless hours watching walls and diving inside myself and missing things out. Trauma made me spend years in a tsunami of distress, sadness and confusion. No much space to just feel alright and exploratory. And feeling ashamed or frightened of happy experiences.
You don't have to wear make up or drive if you don't feel like, but if you do like make up and it's something that you miss, you might try it just alone in your bathroom and not to take the risk of being seen. And progressively feeling more okay with it and yourself. You also can find other things to do.
I had a stupidly long moment just considering to play Metal Gear Solid which for a lot of complicated reasons was emotionally bizarre. It was a game I really wished to have so much when I was a kid but couldn't. So now I could buy it 20 years later, it stayed there for like months with the console sitting in my room. I tried a few moments and while it was really cringe somehow, at a point I just let it go and could find the space of niceness and excitement I did wish to have before. And I was scared of going there perhaps because I was scared it wasn't gonna work. Ways of winding oneself up with small things innit? But honestly it's therapeutic.
And I'm happy to now enjoy myself like the kid I was before should have been and didn't get to be. As much as some people would find it "regressive" because really there is an element of childhood, I find myself much more comfortable with myself in accepting that and just pace up with that loss of time instead of telling myself it will never find compensation and repress it because it's cringe. I call those moments "let the kids out". It's sweet.