I think a good way to introduce a teenage kid to program is a cool platform. And the coolest platform for a teenage kid might be to program something for their iPod Touch or iPhone, because they will be able to show off their work to other kids and will really open his eyes to the potential of the device they usually just carry around to listen to music and talk on the phone.
Plus, they get to use a really cool development platform (XCode + Interface Builder) with a really nice programming language (Objective-C), learn about OOP, can do some stuff in C, there are some really good tutorials on the Apple Developer Connection site.
Even if he doesn't end up writing an app to put up on the iTunes store, he can just play around with stuff and load it onto his iPod or iPhone. I would have loved to have something like this when I was 13; instead of just writing stuff that only I could use, with no one around to see how cool it was, I would have been able to show it to my friends.