Make him do some level design, for example he can create Doom levels. It can also be paper/board games if he is into it. He could make some rules variations t

Make him do some level design, for example he can create Doom levels. It can also be paper/board games if he is into it. He could make some rules variations to an existing game. Nothing alarming here. If he has peoples to play with, create a story, add some rules, play it with the body or lego or whatever.