Since you are very young, and just starting out, get Photoshop Elements 3 to start with.
You can do very many things just like in Photoshop, and this will get you going at a price you can afford.
If you find that you learn every tool in Elements, and can use them, and still need more, then save your money and buy the full version.
You will probably be ready to graduate High School before you reach that point, and if you go to college, you can buy the educational version.
In the meantime, First, download and play with the Trial version of Photoshop Elements.
THEN, download and play with Photoshop(AFTER the trial version of Elements has expired). This will give you about 2 months of experimenting and playing to see how you do.
Also, when those expire, download and play with the trial versions of Painter, Paint Shop Pro, Photo Impact, and Microsoft's Photo Image (?). That way, you can play for quite awhile, and learn about layers, channels, cutting, pasting, painting, and various other graphic tools and applications without spending a single penny!
You will then get a better idea if graphics is really something you want to invest a lot of time, energy and money into.
You can also download The Gimp, which is a freeware photo editor very similar to Photoshop. It does not expire, and I've seen some very impressive work done with it (do a web search for Gimp gallery to see some examples).
ENJOY!
Good Luck!