I am listening to an interesting audio book called Outliers at the moment.
It turns out that being a professional ice hockey player or football player has more to do with which month you were born in than skill and the same goes for many other areas of life like academic success.
If you are born in January (or September in the British system) then you will be the oldest, biggest, most mature and developed in the group when talent based selections are made in the early years of life. It is these people who get selected and then given the most training and the best opportunities for development during their schooling, lives and careers. It simply snowballs from there.
Interesting stuff and it explains why MK (birthday 10/01) is so good at ice hockey