Every age verification scheme is really an identity verification scheme, "age" is just the acceptable entry point. Once the infrastructure exists to verify you are 18, it can verify you are not on a watchlist, verify your creditworthiness, verify your political associations.

You are not building a parental filter. You are building rails.

"Protect the children" is the canonical playbook for every surveillance expansion since forever. The children get protected for six months. The infrastructure stays forever.