Would be very tough to implement in the US, as proposing any sort of "national ID" is pretty much a nonstarter, at least up to this point.

States could do it, and maybe agree on some protocols so that things like privacy-preserving "age verification" could be done.

Maybe the feds could push it like they did with speed limits: make federal funding contingent upon adopting e-ID. Would still get a lot of pushback.

The problem with e-ID is its focused on identity verification, not just age verification and that's where the problem lies.

We still need the ability to be psuedoanonymous online. We should be able to verify age without divulging any identifying information to the service requesting age verification.

An e-ID registry could work on a sort of public/private key system so long as the services requesting informatino from the registry only receives a yes or no of "is this person old enough" and no further information.