If he's the type of kid who likes challenges...and you have a couple trees in your lawn or in a park, buy him a slackline sometime.
My kid's in college, but when he was about that age we bought him a slackline and he and his college aged friends, will still string it up in the yard or at a park and play with it. I think it's the challenge of mastering it, plus it's a good "core" exercise in that it challenges your balance.
My 3 boys are not inside kids, even when they were small they always preferred outdoors and sports. We have video games but they are not obsessed with them, I’ve never had to restrict use, the same thing with t.v..
Is a slackline the same as a zip line?