Hey; I've been working on my game since I was 16; and though I'm not finished yet, but it's getting closer. There's no reason to not start early! And there's no reason to believe that a 15 year old, might not be able to pull something like it off, but it may take a while (for me, to the tune of about 6 years).
11, however, seems to me to be a little young to start up though; making graphical games generally requires math that you don't get introduced to until about Grade 9 (Trigonometry and the idea of the Cartesian plane, as well as algebra); and to be honest, even at 16, programming anything beyond a console window was pretty daunting.
In my opinion, if you're 11, I'd sit on the idea for a few years; maybe refine it a little by writing up a detailed storyline and feature list; or maybe do a small amount of programming in your spare time, aiming a bit lower, and making more simple games like tic-tac-toe, or if you're feeling really adventurous; 2-player human-human chess. Or maybe use some sort of graphical program like game maker, or somesuch. Beyond that; I'd wait until late high school before you really start anything like an MMORPG.
