A lot of you seem to be getting all nostalgic in your early 20s..
I think you're probably just getting to quarter-life-crisis!
It may not be as strong as the mid-life-crisis, but I think there's a definite period of missing childhood, lacking direction, and feeling a little bit lost and unsure during early-to-mid 20s. This is only going to make nostalgic thoughts stronger..
There's a lot of fun to be had as an adult/grown-up - sex, independence, money, a brain that can think deeply, a heart that can love beyond the child's love for mum & dad and the teenager's infatuations - sure loads of things become more complicated, but so what? Lots of it becomes background noise after a while.
Also, this world isn't the rose-tinted world of the past, but there's plenty of fun and beauty in it - we're all richer, safer and healthier. There have ALWAYS been chavs, or whatever you want to call the layabout part of the working class - BUT at least now the majority get somewhere to stay and enough to live on, instead of committing crime to survive.
It's all good people, there's fun stuff yet to come, however old you are...