That said, as a parent to teenagers, I don't know that I believe that age verification is such a terrible idea. The reality is that there's a lot of fucked up porn out there and blocking it effectively across all networks and every device is non-trivial. I understand this is a minority viewpoint on HN.
Of course I have absolutely no interest in uploading scans of my drivers license to porn sites so I don't know what the right answer is. I'm sure there's some cryptographic scheme whereby a 3rd party could verify my identity without knowing for what purpose and then the porn sites could validate that verification without disclosing who or what I'm doing. I dunno.