Governments already have everyone's ID, including DOB. They say that the problem is non-adults accessing adult sites and services. So therefore, the sites need to know that users are over 18 (or the selected government age). There should be a standardized government ID service/API that allows a person to let it disclose their age (or other user selected information) to a requesting site/service. That's all that is ne…
Yes that's how it's done in France for instance, and generally how it's being discussed in the EU.