If you want to actually enforce age restrictions that can be checked via some kind of digital identity I don't see how we can avoid the "trusted" hardware requirement.
The key material must be DRM'ed, especially if some ZKP solution is used.
Otherwise all underage kids would download the cool older brothers private key and load it into their GNU Taler client, buy wine and be gateway'ed into heavier Stallmanisms. Before soon EMacs would be all the rage in highschool.
(Of course we can argue the bigger points, if X should require age checks, or if this even should be done digitally etc. But there's a reason why we don't allow the physical equivalent of self-signed keys for physical ID's, they're not trustworthy)
The key material must be DRM'ed, especially if some ZKP solution is used.
Otherwise all underage kids would download the cool older brothers private key and load it into their GNU Taler client, buy wine and be gateway'ed into heavier Stallmanisms. Before soon EMacs would be all the rage in highschool.
(Of course we can argue the bigger points, if X should require age checks, or if this even should be done digitally etc. But there's a reason why we don't allow the physical equivalent of self-signed keys for physical ID's, they're not trustworthy)