dude you sound pretty young.
If you're about 13 now,by the time you're like 24 high funded 2d games will be a thing of the past. I really doubt that you will be developing in 2d if you're going to go into such a competitive business.
umm i dont know much about directx.
But i think of opengl as just a bunch of libraries that handle input and 3d output.
It doesnt make your graphics better, it renders your 3d graphics.
(i'm correct, right?)