Yes, the age-peer thing is an interesting aspect.
When my son was in school, in First Grade he was held back... (his learning disabilities).. so he would be older than many of his age-peers.
I have seen threads here about other parents who think their young child is academically ready, and might want to be challenged, who are thinking of having their child moved forward.
On those threads, I have always posted that the parent should really be thinking ahead, long term, to high school, when that 15 year old girl is in classes with 17 year old guys, and is wanting to do everything that her older classmates are doing. Or that very, very, smart, but possibly developmentally and socially immature 16-17 year old boy is graduated high school, and is facing college, or 'the real world', if they might not yet be quite ready.