There's nothing harder than calling it quits on a sport. I had two buddies in college who had to finally hang up the skates after concussions... usually it was after 5 or 6 over the course of their hockey career. Its rare to see a player who only has gotten 1 concussion, because once you get one the next one comes easier. It's a hard decision but there's only one right answer for this young man.
Such a tough situation, I wish only the best for the young man, no matter what he decides. I still miss playing everyday, and I am 29 and got to play all four of my years in college relatively injury free, I can't imagine having it taken away.