I developed what was diagnosed as a "chronic, recurrent sublocation of the right shoulder" the beginning of Junior year in high school. At first, it was incredibly painful. After that, it was a conversation piece. I could pop it in and out at will, complete with a clunking sound that could be heard across the room. But it ALWAYS came out when the arm was extended above the horizontal. By senior year, not only was I back on the basketball court, but I'd learned to play defense right handed (I'm a leftie by nature) because my vertical reach was a good 4 inches farther with my right hand, due to the shoulder. Blocked a whole lot of shots that year. If I could have controlled the ball with my right hand, I would have been a dunkin fool. Unfortunately, I couldn't. And if I got hit wrong with it up and out, man was I in pain.
The shoulder did keep me out of the service (I tried to enlist in the CG, then was called for the draft at the height of the Vietnam war).
But once I was no longer involved in any kind of athletics, it never really bothered me more than a few times a year. But that eventually became 4 or 5 times a year, then 6 or 8 times, and now that I'm officially an old codger, except when I'm able to keep my right elbow tucked tightly to my side, I'm in pain. If I need to raise my right arm more than shoulder high, I need to use my left arm to do it. I've investigated surgery (need a full blown replacement), but the 6 months of recovery they are talking about is kind of off-putting at my age.
So yeah, the kid needs to get it done now, lest he end up a cranky old man with a painful shoulder.