Depends on what you want to do on what path you should take. Whatever the case is you're 15 and you have a lot of time.
First off, unless you want to be an artist Flash is not the way to go, and even then there are better things to do. I would say in any case the best thing to do would be to start with some PC game you like that comes with an editor and start playing that game. After you've beaten that game and got some good experience with it then start playing in the editor.
Some good easy games that art good for starters are RTS games like Warcraft III or Age of Empires III. After getting to know those editors and just the very basics start looking at your FPS games like Unreal Tournament, Half-Life, Doom, or Quake.
If you're thinking you want to go into art knowing things like 3DMax, Z Brush, and Photoshop are great but the thing you want to be good at beyond *anything* else is life drawing. Take life drawing classes and just sit in a park and draw. Don't draw from pictures, draw actual real life and just keep doing that. Being good at life drawing will bring you farther than being an expert in any of the above software. After you get good at life drawing, take some sculpting and color theory classes. By the time you get good at those you'll be an amazing artist and learning the above software will be nothing.
If you want to go into programming learn C and C++ above everything else. People will try and tell you that C# and Java are the wave of the future but they're wrong; everyone uses C++ and that's not changing anytime soon. I'm not saying don't learn other languages (because you definitely should learn as many as possible) but C++ is the important one. Don't worry, once you learn one language it's easy to apply concepts to every other languages and all you have to learn is the syntax.
Also, if you're planning on doing programming you better love math and physics because there is a lot of that involved. Just throwing that out there.
Lastly, if you want to go into design (what I do) start playing games and building levels. When you play a game look at what you like and don't like and figure out how you make that feature better. If you like something, try to figure out exactly why you like it. When you're walking through the level try to notice how you walk through it and what's making you move that way (flow). Take note of the mood and how it's being expressed. There are an insane amount of subtle things that go into a level and you need to know all of those.
You will also want to make levels. Like I said, start with something easy like an RTS or even Neverwinter Nights and then move to an FPS game. Personally, I would suggest starting with Unreal Tournament 2004 (not Unreal 3) because there are a lot of good tutorials and books available for it. Don't bother with making 10-20 minutes goofy little games because those will not do you any good. Just make levels and then put them on the community websites. See what people think of them and just keep making levels. When you finally feel like you've gotten all you can out of one editor, try another.
If you're going into design it is also good to know art and programming software. You don't have to be amazing at both be definitely need to be proficient.
Hope that's a good start, say what you actually want to do and I can probably give more advice if you need it. Kind of keeping it general at the moment.
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And a lot of people are mentioning things like gameMaker and such and while those are a fine start just like an RTS you want to eventually move to an FPS engine. It doesn't matter if you don't like FPS games or not, what matters is you're working in a 3-D space and getting to know how to use and apply concepts.
Also, if you're going to do something 2D use Torq Game Builder. You have to pay for it but it's really good and you can use it with XNA if you ever really feel like it. It doesn't matter a lot what you start with, you just want something to get your feet wet before you dive into a full 3D editor.