It all depends on the child’s emotional and educational development and Not Sports! A lot of that has to deal with how you prepare the kid.
It is kind of early to assume your kid won’t be able to attend kindergarten at the normal age. My daughter was an August birthday and she had no problems. I have a late November birthday and started school when I was 4, college when I was 17.
It is sad how many parents hold back their kids just for sports. Also, crediting Minnehaha as a sports school because they had one small group of kids in one sport transfer in is a stretch.