I believe that the only way to be truly great at something is by pursuing it relentlessly. Motivation, focus and determination is definitely more important than how "gifted" you supposedly are. This is even more true if the person in question is still a kid.
To become a good writer, writing a lot is the only way. To become a good painter, you have to paint a lot. To be the best programmer you can be, write as much code as you can. To be the best athlete, train harder than everyone else. This is being mentioned time and time again, but still people in general don't seem to get it. It's always "she's so talented" or "he's so lucky to be born with that gift" and so on. Of course natural predisposition plays a part too, but I don't think it's as big as people seem to make it.
The hardest thing with getting truly good at something is to give up, or at least cut back a lot, on all other activities. You need focus and have a clear goal, something to pour all your energy into. You have to want to be the best at what you do and only have that in your mind. Focus is the key.
This is a huge problem when you want to be good at everything. I just don't think it's possible be that. Sure, you can be pretty good at a lot of things, but not great at everything no matter how hard you try. Intellectually, no matter how clever you are, time is the limiting factor to what you can achieve. And the slower you think, the more time you need.
People who push them selves to extremes impress me. Not so much for the thing they chose to do, but for their ability to take on something truly extreme and just do it.