I'm about to turn 25.... and I'm probably what you would call "settled down" (long out of school, full-time job, almost married, etc).
I still LOVE to go out and party, but it's just not feasible anymore. By the time it gets to be 11 or 12 on a weeknight (Friday, too)... I've been up for almost 18 hours and I'm just too tired to do much but be a lump on a couch.
If I didn't have to work, I'd probably be out every night. Unfortunately, I don't think coming into work half asleep and hung over would keep me my job very long
At the same time, I guess I do look down on some of my "less settled friends". I don't mean to, but when they're in their late 20s drinking a 12 pack every night, working at the Stop N' Go for 6 bucks an hour, and then complaining about how much their life sucks, I want to shake them and say "then get your head out of the bottle do something about it".