I'm not so sure that kids/teens should really bother learning the low level sorts of stuff. Now, I don't think that it isn't important to know. Certainly, if you are ever working in any sort of embedded system you will need to know this kind of stuff. Even if you aren't its helpful to know, but if your a kid playing around in your spare time its really not important to know. My suggestion would be to find something you find fun and do it until it gets boring or you find you need something with more power. I started in HyperCard. It was easy to do some simple stuff and while it certainly wasn't the most powerful environment it was cool to do stuff in, and if you don't know the first Myst game was a HyperCard project. If you like doing stuff with the Web then start with HTML then maybe Javascript or Pearl.
Personally, I think the Flash environment would be a great place to start, though its kind of expensive for a kid to play around with. That said you can easily make some cool things in it, there's lots of books/websites which can help you, and once you've completed your first masterpiece you can easily post it on the web to get real feedback. Which can be incredibly useful. You could then see the whole project life cycle.
Later after you get out of high-school you can go on and get into a Computer Science program and they will cover all the various things you should know, the low level stuff, the OS stuff, 3d graphics or whatever else. I'd suggest a Computer Science (or Engineering) program over a technical college since a college tends to only teach you the language of the day rather then the theory behind everything.
The important thing if your start out is have fun. If you like doing the lower level stuff, go for it. Though I think most kids would rather be able to see instant results, which to me would mean something like HTML or Flash would be better, but to each their own.