Australia

There’d have to be a way of checking people’s identity, and thus their age, whenever they create an account, and it would have to be legally mandated for any online sites where people can post user-generated content. Of course, this would eliminate online anonymity, so as long as we see ourselves as less oppressive than Communist China, there would have to be mitigations to say that we’re not really eliminating online anonymity. Perhaps some sort of third-party age verification agent, which would check identity and just let the sites know if a user is verified to be over the age threshold. This would have to be strictly regulated to ensure data doesn’t leak.

Of course, given that this is Australia, the police would have access to the mapping of people’s identities to online accounts, though under strict safeguards to ensure that this access is only used in the direst emergencies. Of course, this being ‘straya, the safeguards would be like a locked gate on a path with only a KEEP OFF THE GRASS sign preventing the cops from walking around it. Within 18 months, a cop will have used this to put the frighteners on his ex-wife’s new man or something similar. Within 3 years, all pretence will have been abandoned and everyone from the ATO to local councils will have access to the real-world IDs of people’s online accounts.