OS-level age indication is the perfect solution. You just enter a date-of-birth at initial device/user setup. It gets stored locally. Then there's an OS-native API for apps to read an age bracket from this. This can then be forwarded to websites by web browsers.
Almost all devices used by minors are set up by parents or guardians. That's what makes this effective.
It's private. It's decentralized & offline. It's effective. Children will be safer online, without harming anyone's privacy. In my opinion, we developers should take the lead on standardizing this properly, and we should use it to counter regulators who are still stuck on harmful online age verification requirements.
You can have your cake, and eat it too.
