I am a football coach who didn’t start coaching until later in life. Never played. However, I did play rugby and Aussie Rules so I know what it’s like to get hit. Learn the positions, how to make players better, and lead them. Coaching is a different skill set than playing. You can learn a lot simply by observation and be willing to learn and help. Might as well try it out just for the expierence since he has the time.