Google, as one example, uses a bunch of information including profile information and behavioural data in sophiticated ML to imply demographics [1]. This is what I mean when I said they already do it.

The suggestion I'm talking about doesn't "solve" the adult content issue. It's more targeted at social media, which I think is the bigger problem. If it's illegal to show minors ads and advertisers can't target minors then you've just removed the economic incentives.

Youtube tends to be included in age verification legislation. Personally, I would be happy if you simply limited advertising and (IMHO) you dind't show commetns.

Roblox I think is on the right path here, at least in theory. Roblox segments users such that you can only interact with people one segment above or below you. The issue with social media (again, IMHO) is in big part that minors can interact with adults and vice versa. Really you want more of a sandbox so people can't prety on children.

[1]: https://support.google.com/google-ads/answer/2580383?hl=en