Good for you. I would suggest you take a class. Many colleges offer them at a very reasonible price.
Not old enough for college, then computer camp is pretty common these days. Take a look around at schools, YMCA and libraries.
If you really want to teach yourself then I suggest you go to the library and get yourself a couple of books. Or go to Borders or any other book store and buy them.
Most programming classes start with BASIC. It is an introduction on how a computer reacts and gets you thinking about how a program is setup.
Remember programming code is a language. If you aren't successful in learning a foreign language, then I would suggest that you just use the computer for fun and entertainment. Because there really is no difference in learning a foreign language then it is learing a programming language.
Just like it is not a good idea to say something in english in your head before commuicating them in another language, it works the same for computer programming. You need to think like a program.
Just a warning...the learning curve is steep. Don't get frustrated if you don't understand something. Also, just like math you need to have a rock hard understanding of the basics before moving on more harder programming.