A kid will more physically mature for his grade if he’s a year older. It can benefit at recruiting time.
I’m not a fan. If a kid isn’t emotionally mature to start school at five hold him back from starting for a year. Our school district tests for kindergarten readiness. Once starting school I’m a proponent of a post grad year on the back end, if needed rather than holding a kid back at the beginning of high school.
i wonder how many kids get held back before high school for athletic reasons then don’t get athletic scholarships.