And face/id scanning aren't as good as the solution that works in the real world for alcohol because they can be tricked by a video game face or a photo of someone else's real ID. Any solution that works online can either be trivially bypassed or adds an unacceptable level of hassle and risk (e.g. leaks being used for blackmail) for legitimate users.

The solution for alcohol works really well because very few children have the ability to get a fake ID or convince people it's real and theirs until they're close enough to legal age that it doesn't really matter much if they drink, and parents have the ability to override it on a per-drink basis if they're okay with children drinking under their supervision, while non-parents can only operate on a very small scale before they risk getting caught. Once people are old enough that they're obviously adults, they don't get asked for ID anymore, so it's only a small fraction of the population that have to deal with any hassle, and a shopkeeper can't memorise every single ID card they've ever seen and then suffer a cyberattack and reveal what alcohol specific people have bought to someone who'll threaten all of them in case some of them are willing to pay to have it kept secret.

Preserving privacy means tokens become trivial to share, and then there's nothing stopping a ten year old watching huge amounts of extreme porn except for things that would have worked without having any system, like having their parent stand behind them. If the new system doesn't improve things compared to having no system, then there's no point making it.