If that is the worry, then bad influences won’t be stopped by some shitty internet-wide age verification. Teens can bully each other with their cameras, or words. If their peers are the problem, no amount of government playing internet cop will help.
No smart phone and no social media for kids society wide and we go back to good old fashioned bullying in person. That’s much easier to curtail.
I don't think that age verification is a good idea. But I don't think the counter-argument that "parents can just monitor their kids' devices" really holds water - there's still plenty of ways around it.
If only parents had a way of controlling who children associated with. If only.