Jen Are people more mature at Uni?
Probably not, but as @Bryan mentioned, it's an opportunity to re-invent yourself. Nobody knows you and you develop new friendships from scratch. That's not to say you won't still see your old friends, but a whole new world of opportunities opens up. The heirarchy and social order that developed in high school disappears, and everyone starts afresh.
Then all the catty bitches in the "cool group" from school get knocked up by their abusive jock boyfriends, and disappear off the face of the earth... Well, they did at my school anyway!! You'll still spot them at the local K-mart for years to come, with their little tribe of junior bogans in tow. ;-)