The way to make a criticism involving their age without being reactionary is to put it in context.

That can be the context of human brain development, pointing out that impulse control and decision making abilities are literally not fully formed at their age. Or the (related) context of the power dynamic between them and their much-older superiors.

It's reactionary to attack the age directly, and therefore denigrate young people broadly. As usual, what matters is the intersection of their age and other factors.