Hi L.,
From your 'about me' section, you don't seem to mention a husband or boyfriend in the picture, so I assume you may be a single parent. If so, I know how hard it is to find time after working 40+ hours a week, taking care of the house, and all the other necessary thigns, to do hiking trips, extracricular activites, etc. If you don't have the funds for extra things or the time, then maybe find out from him what he is willing to do in order to stay more active. We do live in a technicial age, so a video game is going to keep his interest more than a book. But maybe instead of buying him a game that is nothing but pure 'play', the next one you buy should be one that will teach something...from math, to reading, etc.
as far as getting him outside, maybe invest in a pair of skates, bike, pool, something that will get him excited to go outside. When he does go outside now, what occupies his time? What ever it is, play off of that and extend it somehow.
Above all, as others have mentioned multiple time, you are the parent. If push comes to shove, throw the system in the shed till he decides to learn how to be responsible for himself and keep himself healthy.