if you have an average athletic kid at 10-12 years old and start to practice hard, it is probably too late.
But if you started in some scale already as a toddler, then it is different.
My daughter is 2 years old and loves running around, jump, climb, throwing balls....our neithbour girl, same age weighs 4 kilo more (13 vs 18 kg) and is used to be carried around etc, watch tv and eat, eat ,eat.. a bit clumsy describes well her motor activity style.
Neither of the girls would probably make it if theys started serious tennis or sport practice at age 10. But if they start with such activity very early, with variety, some coaching, and many hours daily...the sky is the limit....if both got the same exposure from today, probably my daughter would come out as the more successful anyway, but that might not be "talent", just that we fed her differently and encouraged activity differently from birth to 2 years of age...so it would not be genetic...
But if my daughter practice 1 hr a day, and neighbour girl 4 hours a day, say from 3 years of age to 10 years of age, I would guess she would be the one with better skills
the same with fast/slow twitched muscles, that can also change with lot of training (research fact)