We "academically red-shirted" our 2023 summer birthday boy in 6th grade. He was so smart as 4-5 year old we felt like we had to put him in Kindergarten early. But he was always noticeably a little emotionally behind as the youngest kid in his class. After 6th grade, I had a career change and an epiphany to have him repeat the grade. (I would be lying if I didn't consider the sports implications) Every teacher and the principal told me I was being unreasonable... he's too smart, he'll be bored, he'll get in trouble, etc... We did it anyways. We home schooled him so he wouldn't feel weird. I went fishing and camping with him. Did overseas travel trips. And played lots of sports together. It was a great year.
He's definitely a more mature high school student because of it. Grades are super easy. He's disciplined enough to study for the SAT/ACT every day since mid freshmen year.
I think it will help him out with soccer and baseball. He's little so I can't imagine he would have had any shot if he were on the original timeline. Now I think he might have a shot at high level D3 baseball or soccer. IMO, it was a win to do this.