There are many good textbooks available on the web for free, but I believe the majority are either on more advanced topics or for non-mainstream languages.

http://www.diveintopython.org/ is often recommended to learn Python. I found it a dreadfully dull slog though. You might have better luck with one of the books linked here: http://freecomputerbooks.com/langPythonBooksIndex.html

If you're feeling up to a bit of a challenge, and don't mind more unusual languages, there's http://www.htdp.org/, http://mitpress.mit.edu/sicp/ and http://thinking-forth.sourceforge.net/

I think your teens is a good age to be programming. It'll help you decide if it's something you want to pursue, and if you do, you'll breeze through the first couple years of most CS programs.

Also, make sure to learn C at some point.