For sure. And the trend towards holding kids back isn’t boarding or even prep school specific. My family is all in Texas and it’s become standard for my cousins & siblings to hold their boys with spring or summer birthdays back in either pre-k or kinder. It’s more of a mixed-bag with girls but for summer birthdays at least it’s no longer just assumed that a kid will stay with the grade they meet the age cut-off for. Some honestly think their kid needs the extra year but others definitely seem to feel forced into it, especially if they want their kids to be remotely competitive in the big team sports.
I have mixed feelings about it. To some extent I like the idea of moving past the assumption that all kids will or should progress at the same pace and pattern over those crucial 13 years of school & development. On the other, I don’t love kids who are really ready to move to the next grade being held back because they and their family feel like it’s the only path to their goals.