Heavens no, Dear Reader; if he's a drugged out, zombie-brained, frat-cat now there's a fair chance it can be outgrown. He's only in his early 20's. There are plenty of ex-druggies and partyers who, as time goes by, become less interested and consumed with this lifestyle. Some go on to greatness: Johnny Cash, Anthony Hopkins, Robert Downey Jr. Some go on to heal themselves but destroy other peoples lives: George Bush, 43.
Still, it seems this guy you speak of has shown an early and steady proclivity for the bong and beer lifestyle. He will need to find other ways to 'decompress' or more importantly figure out what he's escaping from. Now I'm no Dr. Drew, though I do run a Celebrity Rehab Clinic out of my apartment in Brooklyn, but if I were you, I wouldn't be throwing all my eggs in this guy's basket. If you're dating your town's Kurt Cobain or Lindsay it could be a painful and frustrating road for you. Be supportive, but be smart; a 22 year-old drunk guy is reasonable, a grown drunk is as vile as THIS VILE HASSELHOFF
Funny Guy
I think an important thing to look for, here, is whether or not he has future plans that seem stable. Is he in school for something viable? It doesn't need to be pre-med or anything, but most people who see themselves as going to college and getting a grown up job one day are usually the folks who know that their partying youth has a time limit.
If, say, he works as a server, loves the lifestyle and intends to work his way up the management scale, you may find it is harder for him to give up partying (I know, not all servers are like this, but it is a culture that tends to spend half it's tips at the bar after work).