I think many 10 year olds have the aptitude to learn scuba diving, but I agree that they don’t make very good "safety" dive buddies. I always suggest that at least two adult divers go along with a younger diver for safety reasons.
I’ve also had to refuse to certify some 10 - 12 year old simply because they wouldn’t pay attention in class. They may be good in the water, but that doesn’t mean they can skip the knowledge portion.