FWIW, my son has an early September birthday. We used to live in MA, where the cutoff was 8/30. One of the advantages of our move to NH was the 9/30 cutoff allowing him to go to K a year sooner.

We were in a very similar situation, where we were very concerned about him being bored and leading to behavior issues. He's doing well in K, though the social stuff is still a work in progress. I'm not sure how much of this is related to going early and how much is because he lost a year of socialization during COVID.

All in all, I'm glad we sent him early, but we agonized over the decision for months and will never really know if it was the right one. There are advantages in both directions. Having the decision out of your hands isn't the worst thing.