Always, always, always wear a helmet when freeskiing. Always. You should probably always wear one all the time while on the slopes, but I feel like that's a choice, and you're old enough to make your own decisions, right? For real though if you're even going to be attempting any hucks or jibs, you've got to protect your noggin with a ski helmet.
Back in the day, I used to pull some pretty sweet cork sevens. It didn't happen overnight though. I would get all sorts of weird in the air right after launching off a massive kicker. This would result in me usually landing somewhere around, or on top of, my head. Thankfully, my mom always made me wear a helmet.