Gymnastics and track for obvious reasons. Strength and flexibility with gymnastics and cardio/endurance with track. I assume a lot fo American high schools have more diversity than in Canada anyways?
I played ice hockey for 12 years before quitting for jiu jitsu and I played recreational lacrosse.
I think gymnastics is the best prerequisite period. Flexibility, strength, balance, coordination, and spacial body awareness. And there's contact too, when you fuck up. You just gotta smack him in the mouth when you see him to keep his head in the game. Guaranteed he won't do it though.
4 years blank slate, interested in MMA. He shouldn't refuse to wrestle. He's gonna have to learn eventually, starting now will be ideal. What reasons does he not want to wrestle?