There's a town near me that historically has a very strong high school football program. I was told recently that parents are encouraged to wait until their boys are age 6 before starting them in Kindergarten so that they'll all have an extra year of growth by the time they reach high school.
I guess this would avoid the eligibility issues or even the social stigma of repeating a grade. However, I sure have a hard time thinking HS football is so important that you'd do something like this.
And, let's say you end up having a college and pro career later on. Doesn't that extra year take one year away from your professional potential?