Penis Development During Childhood

I think it is a safe assumption that most infant males are born with the same size penis (or very close to the same. I haven’t ever seen a baby boy with a 9” penis). It would then make sense that something has to drive penis size during a boy’s growth years, probably 0 to 15 or 16. Does anyone know of any clinical studies that have determined what influences, genetically or otherwise, determine penis size during these years? I’m curious if it is genetics and natural development, chemical, or hormonal. There has to be a medical explanation why some guys wind up with a 10” penis and the majority get a 5” penis. I’m looking for real medical data or information here.

We depends on genetic but if we have good life style it helps a lot, for example during these stages a person who smokes will have more problems than who do exercise, may be 1 or 2 cm diference.

Black guys average is up to 15 cm and coreans only 10 cm.
We are programed since we are babies but of course we can improve this using PE.

But if you have small penis and doing PE you gain a big size, your children will have small penis.