We have two children who repeated - one repeated PK4 and the other repeated kinder. Both are summer birthdays so they would have graduated at 17 if we had not held them back and they are each on track to graduate now at 18 so I don’t consider them “older” than their grade. One has ADHD and, even though we didn’t have it diagnosed until middle school, it was obvious from very early on. We decided to hold her back because 1.) she was young for her grade 2.) we moved so it was easy to start over in PK4 again and 3.) she was just so unfocused that we hoped that the extra year would help. She is doing great. Definitely still has ADHD and I’m not really sure if holding her back “helped” anything but zero regrets. She’s slightly “old” for her grade now, but not by much. My other summer birthday child we also held back. He repeated kindergarten. He was just super immature and he’s also very small in stature. I do think holding him back helped him by giving him more time to mature…but he’s always going to be short. He’s doing great and he’s definitely NOT old for his grade as all summer birthdays in his grade were held back.
So, overall, I’m a fan of taking extra time.
Having said that, my husband was held back in middle school and did not like it. The reason they did it is that he was young for his grade. He lived in two different states during his childhood and each one had a different age cutoff. They moved back and forth between them twice. When they finally settled down in the state where he would finish school, they held him back so his age would align more closely with the kids in his grade. But, he really didn’t like it because even though they changed schools when he did, he already knew a lot of boys from sports and he was embarrassed to be held back.
Whatever you choose, I think that most kids are very resilient and will be find whether you hold them back or not. Good luck with your decision.