teach him to tinker existing sites in browser with javascript. Once he is able to see the changes he is making in realtime it will get him hooked, then you just need to point him to the right references here and there and he will become proficient on his own. I have taught or rather i shoud say given a demo to number of kids and i am yet to find a kid who didn't get hooked. It's kind of empowering just to change the background color of any website to your liking :)