Even if perfect age verification is implemented, kids will be harmed. Because they are vulnerable while above the arbitrary age limit. So -arguing for age verification is harming children. Won't somebody think of the children?
And the answer comes back to the same point. Parents should mediate this. Online content should advertise its maturity level, and parents should be able to configure devices at setup time for the maturity level they are appropriate for. Then apps should respect that and everyone can be better off without robbing everybody of anonymity or freedom.