I have told this before, however lots of new people here. My son has a Birthday in Sept. He started school what many consider very early. We knew he had good hand/eye coordination, but had no idea what an athlete he would turn into.
As he progressed through the school system he was also identified as Gifted by third grade. Once he started playing baseball in middle school, we found out many of the kids a year behind him in school were a year older than he was. Many of the parents started their kids a year late. Mostly for athletics. Son, was always well adjusted, made good grades, and got along well with his peers. As high school got closer people started asking us if we were going to hold him back, since he was smaller that his peers.
We never considered it. He did very well athletically and academically. Plus later we learned when another parent tried it, that the school system in no uncertain terms would allow it. To repeat a year he would need to go to another school system. And we really liked his public school. And it has a great reputation, with colleges.
So we kept him there and he went on to play in college in a D3 conference. Started all four years. Most of the players in the class behind him either chose to not play in college or were never recruited.
Over all I would probably make the same decisions. I do not think the extra year would have made him a D1 player.