I disagree with everyone here on the most part.
I believe (of course, based on myself) that
grit is the main factor in how people become good mathematicians. I'm new to maths but if you're motivated and have realistic goals you can become a ace...no matter what.
Grit. It's a personality trait whether that is genetics is another issue.
http://en.wikipedia.org/wiki/Grit_(personality_trait)