I started playing the trombone in 5th grade. I got braces the day before I started high school and got them off the day before I left for college. Yep, four years. You get used to it. In fact, by the time I got them off, it was weird playing without them. Don't get me wrong, I split my lips a few times, but they toughen up. I was playing all the time though, so if he's playing more passively than I was, he might not adjust too quickly.