Our cutoff is September first. My son’s birthday is August 28th, so we held him - on the theory that he was a little short for his age (still is), of pretty average intelligence (still is) and that a year wouldn’t hurt. I’d do it again (although he’s going into his Junior year and sometimes I think that he’d be graduating this year and I’d be done with him in high school!). He is one of the oldest kids in his class - redshirting being uncommon here.
My daughter’s birthday is September 20th, so she is one of the oldest in her class as well.
I have a friend who has a master’s in remedial English - so she’s dealt with kids trying to catch up her whole career. She says she’s never seen anyone regret “redshirting” - she’s seen a lot of kids who would have benefited from not being the youngest.
But me, I’d be cautious - even with the three days the fact that he is supposed to be a grade above carries a little stigma among the kids - like he wasn’t bright enough to start, or was held back. I wouldn’t do it if it were months.