yeah if you just do a normal session there will be people sorta around your age, i went to HN three times and usually there were a couple people around 22-25ish, a ton around 16-21ish.  the people at the adult sessions were  like 35 to like 50. and they werent like cool 35 year olds, they were like the buisness type guys, with gaper gear and stuff, some were pretty cool, but your gonna feel like your hanging out with your parents if you do that.
and yeah i think anyone over 18 goes out and drinks and shit.
it seems like ages 13 to around 30 is like its own age group anywhere if you know what i mean.  like we are all into the same music, clothing, sports, same attutudes etc... and espeically at a camp it shows, cause everyone is cool with everyone.
like a couple of my good friends are getting close to 30, and they are almost 10 years older than me, and ive got alot of good friends like 5 years younger than me.
 as long as your not one of those guys who turns into a complete sell out when they get out of college and goes straight to buisness suits and shit tons of money, you will fit in fine with the rest of that "age group"