I don’t think I’ve ever seen a single suggestion of a way to implement age verification that isn’t a privacy nightmare. Oftentimes they literally just want a credit card number, the assumption being that a child would never be able to get hold of such a thing.

In some of the worst cases they actually want a passport or other government ID sending to some organisation that would verify you. With all the fun potential data breaches that that would ensue.

Most of the time these rules never get off the ground because privacy advocacy groups basically sue over it and win every time.