The article didn't say that these age differences were adjustable defaults, so I would presume not. If Apple put in these restrictions to protect the privacy of older children, making it adjustable would defeat the point.
(And by the way, I respect Apple's desire to protect children's privacy from their parents, but forcing the change at 13, for everyone, seems awfully prescriptive. It's fundamentally a parenting decision, and Apple should not be making parenting decisions.)
But if this can in fact be controlled by the parent regardless of the child's age, that does resolve the problem!
