easy.
Look into some clubs through your uni. There is probably a ski club, ultimate frisbee is always fun, cycling, perhaps even film or something like that if you're into it.
Also, someone above said it, but I'd try it a bit differently. Think of some activities that you can have fun at and they can have alcohol if they really think it will improve their time. Just become the activity planner. Every group needs one, otherwise you end up as the lazy livingroom type people. Bowling, cliff jumping, camping, river floats, climbing, even a pub trivia night. All those things are super fun with out alcohol and typically keep the people who are drinking a little bit more in line. Also, who the fuck turns down a river float or bowling night? You can be ridiculously lazy and here one of those and be on your feet in 5 minutes.
Sometimes it just takes some initiative. You're getting older. Sometimes if you want to have fun, you need to take the initiative. You're friends will only get lazier.
