An interesting question. I think a huge chunk of it is how much you were engaged with high school life. I wasn't very at all, I didn't really hang out with anybody (outside of class) but nobody bullied me either, I was just sort of apart from it and largely by choice. People who really dwell in their high school years are, I'd say, the ones who either were at their social peak - think the stereotypical quarterback Chad/prom queen Stacy - and the rest of life never measured up, or they had a really bad experience (was a freak, bullied, embarassed themself constantly) so they have some "trauma" (not real trauma, I mean, but gay sissy trauma) from it. I rarely think about high school and when I do it's generally with mild fondness for people I remember from it. But I knew it was bullshit at the time and I remember liking some classes a lot but often just feeling tired on getting home. It was bullshit and I thought (still think) it was a waste of my time and I could have done better things on my own, but didn't hate it.
College was when life felt good, I didn't work for money during it so in a way that was just extended adolescence but I did have a circle of friends I hung out with and I loved class and even when I had to do things I didn't like it felt a lot better because I was there by choice. You're not a slave at that point. So college was like the perfect world, because I got to live alone and do adult things while still really just being a kid. I felt like I learned much about myself and living in college, like the world actually opened up to me instead of being some dull mirage. Ayn Rand wrote about disliking childhood and I think my view on it is a bit like hers, I wanted to rush into the adult world. Now I wish I was in extended adolescence again. I have no drama from college but I do have regrets about mistakes I made in how I interacted with certain people, particularly one friendship that I think needed to be ended but which I could have saved if I had known better at the time, one that I should have kept up with but let pass, and one that I think I was not real good to my friend in.
Graduate school (since most people don't do graduate school, this is where it stops being relatable) feels more like the shitty high school experience than high school did, because although I did pick my field and I do want to finish it now, I hate most everybody around me but (unlike college) have to deal with the same people semester after semester, and no friends outside of it, and the work feels shitty and pointless, the only stuff I've really learned is what I've taught myself. And then there's that awful feeling that I've spent a third of my life expectancy on this and now there's no more time to delay Real Adulthood. It's funny, too, I used to feel like an old man in high school, then I felt like an adult (though in hindsight it was more like a teenager) in college, and now I feel like a high school kid! Despite living far away from home and living on my own salary I earn working for the school. It's the social atmosphere, I think. Being a loner actually has some big upsides, because if you don't involve yourself with normalfaggots much then you aren't susceptible to the pressures they put on you.
I think that we all have a desire for freedom. We also all have appetites, and appetites grow when they're filled and shrink when they're denied. To be a loner and to stay a loner, the appetite for socialization stays small, but to be a loner and then branch out into having a fulfilling social life, and then to lose that, the appetite has grown and now it is a stressor that didn't have to be there. But to have never done so denies a lot of the richness of life. And I have a suspicion that the angst of a high school kid comes not so much from their age or their "hormones" or all that shit but from the phase they go through of having to interact with judgmental and cruel people for the first time, little kids having a capacity for cruelty but one that is fleeting, that comes from thoughtlessness more than being calculated. To go from a small circle of people who, despite some flaws, are essentially honest and good to a circle of phoniness and backbiting and social jockying is cruel.
None of this really has anything to do with the question OP asked. I think too much for my own good and these are thoughts I've chewed on for a very long time.