Make sure that he's playing games suitable for his age group. All video games are rated and labeled by the Entertainment Software Rating Board. Steer clear of any rated "M" for mature. Those are for ages 17 and older and can contain heavy-duty violence, strong language, and sexual content.
Keep the video game console in a common area of the house, not your son's room. That way you can catch any inappropriate content in the games he's playing, and he'll be in a position to interact with others in the house while he's playing. Also pay attention to time spent playing games on smartphones and tablets.
Make sure your son has appealing alternatives, too: sports, activities, opportunities to socialize with peers, and downtime to be creative. If you continue to have concerns about his video game activity, talk with your doctor.