Unfortunately every 13 year old (girl or boy) likes to watch TV and listen to music

.
What else is he interested in? There's gotta be something else other than TV and music.
What kind of personality does he have? Do you think he will be successful in a sport? There are SO many types of sports out there that even if he's not into the most popular options (football, basketball, baseball), there's still lacrosse, swimming, hockey, track/cross country/running, even badminton and ping-pong!
Then there's acting, singing, dancing... Be sure to leave all the options open and let him choose something he might like to try.
You said he likes music? Then why not try to get a few friends together, rent or buy used some guitars and maybe a drum (you don't necessarily need the whole set

) and try a band. They can start out learning some of their favorite songs and maybe even write some of their own. If they practice in your home, though, I would be sure to buy earplugs. They are going to sound horrible at first, but it's only up from there! (hopefully!!!)
And even while you may have to give him a little nudge to put down the remote, make sure that you don't push him into something, because that could (and will most likely) end in failure (and he'll hate you).
The MOST IMPORTANT thing to remember is to support him in ANYthing that he does. At such an impressionable age (even though he may not think so), he could still grow distant and decide that your ideas of a hobby are NOT what he had in mind (if you know what I mean)
Anyway, GOOD LUCK. Remember to be polite and only nudging.