There’s also the potential for bullying. Not every older kid has leadership skills/potential and more than a few lord their age over the younger ones. That bossiness turns into bullying very quickly if the coaches aren’t on top of it. Both the junior and senior teams at different gyms my daughter has been on had bullying issues that went on the entire year in large part due to the age gap. The coaches can’t catch everything and I’ve found the whole “zero tolerance for bullying” thing is just a platitude, not something that is followed through on.
We had a girl on the team last year who would constantly scream at and berate her teammates, and would go so far as to regularly pinch and dig her nails into her much younger flyer’s legs as punishment if she felt she wasn’t tight in the air or whatever. This bully that all the older girls despised for her screaming and the younger girls were afraid of remained on the team even after the coaches were made aware of the physical abuse (they had to have been aware of the verbal assaults). The younger kids are often too afraid to say anything.