damn dude, like i had fun in my teenage years and all, but im so glad that shits over with. the amount of freedom we have now, and the attitude i and my friends have is so much better. Im more active than ever now, instead of hanging out at one of our houses watching tv all the time, we go camping, mountain biking, skating etc... all the time.
ive got friends out of college, and some who arent going to college and just working, but it still leaves us more free time than we ever had in highschool.
sound like you just need to realize that your still only fucking 22. in 22 more years you wont even be old yet. and you have a good 10 or more if you want years of very little responsibility and fucking around having a good time doing whatever.
ive got friends like you who think that being over 20 means they have to get serious and stop having fun, but its the ones having fun and fucking around all the time who are making more money, and their jobs/lives are looking to be more successful and fun than the guys taking it serious.
stop listening to negative people and listen to positive people and think about how much the positives outweigh the negatives, we have such a better situation than we did in highschool to do cool stuff and have more fun and do more fun things than ever. and its the people who dont realize that and spend the next 20 years being serious and mopey about it that look back and say "i was so young back then i wish i did more"