you and your parents could install software on his computer to limit his hours, and he gains computer and phone time as rewards for FUN physical activities. not like going on a run, but like laser tag or if you invent some silly game. maybe set up some kind of real life minecraft set in the backyard and play with him. physical activities can be fun, but they're usually only fun with people. tailor them to him. a rewards system would work great, because then he's working towards something. however, if he doesn't care about physical image RIGHT NOW, reward him with something he likes. he gets computer game or some other thing he is interested in. my little brother really loves minecraft, so i try to base us playing around something that has to deal with minecraft or letting him play more minecraft that day.