Hm ... Do you play other boardgames with him? I'm thinking Chutes and Ladders, Candyland, that kind of thing. Given that I just introduced my kids (7 and 10 at the time) to
Kingmaker, I think you need to start slowly. And even that will take a few tries. They started playing Stratego a year ago, I think, probably because of my enthusiasm and because it's pretty easy to pick up. The other day, I heard them talking and looked into the family room to see them playing Stratego. I don't think they finished the game, but they did pick it up independently of me, and that was pretty cool.
So, I guess the progression is Candyland-Stratego-Avalon Hill. (Although
France 1940 was kind of a big step up and was a bit too complicated for a seven-year old boy). They do enjoy Settlers of Catan, though, come to think of it, and asked if we could all play soon.
The important thing, I would think, it to just spend time with him playing games, perhaps the ones he wants to play that can shape his mind to enjoying what you want to play, eventually. So, games with strategy of some sort, however rudimentary, and some thinking versus just flashy lights or pretty pieces and sounds.
Edit: Of course, Kairtane says in one paragraph what it took me three.