Muscle type you possess is pretty much given and make difference between talented sprinter and talented weight lifter (speed vs strength). Possible body flexibility depends on muscles and joints too and you can influence it only up to the point. You can do only so much to make your attention span longer and better attention span is advantage in some sports too (say race driving).

Whether your body can sustain extensive training or whether it will break depends partly on your genetics too. If you are low on red cells in blood, you will be at disadvantage too.

Bigger hands are an advantage in swimming, longer hands in climbing. Some people learn technique easier then others although I do not know what is the difference there. Your sensitivity to pain is not only a question of will power, it depends on genetics too - lower pain sensibility is advantage too.

There are plenty of individual variances that make difference between who can succeed in professional sport and who not.