It's not clear to me that every site would have to perform age verification themselves. Seems like the "I am a minor" flag could be managed at the client operat

It's not clear to me that every site would have to perform age verification themselves. Seems like the "I am a minor" flag could be managed at the client operating system level (e.g. as a property of the cell account on mobile devices, or as a property of the user account on a laptop or desktop machine), and transmitted per-request (e.g. in a HTTP header).