Tanith Lee 
Don’t Bite the Sun 

It’s jang to be wild and sexy and reckless and teen-age. It’s jang to do daredevil tricks and even get killed a few times…you could always come alive again. It’s jang to change your body, to switch your sex, to do anything you want to keep up with the crowd. But there comes a time when you begin to think about serious things, to want to do something valid. And that’s when you find out there are rules beyond the rules and that the world is something else than all they’d taught you.