Ask him to found a club by himself in the school ASAP.

My daughter had the same problem as your son before. She was 2 years younger that her classmates in her high school. She ran for a chairwoman or president for several club,but no body voted for her. She has to found an Asian Culture Club under her 5 friends' support. Therefore, she was a founder and president. She arranged some activities such as visiting Japanese museum and Chinatown, dining in some Asian restaurants, etc. till she graduated. I also made some sushi for her club once.

So, your son can ask his friends to help him to found a club, and arranges some activities till school finishes. Or,try to be a captain of junior sports team (JV）. The coach can point him to be a JV captain when he is a senior if he has good relationship with coach.