That's the thing, you shouldn't have to.

But it could be used that way. The problem is, the types of certificates that I'm suggesting would offer no privacy at all, as they would have your real name associated with them, and they'd be issued by the government...essentially, the exact same idea as DoD "CAC" cards.

If it's the type of business that you want to supply with that info, that's one thing. But it would eventually, be compulsory, and that's not really what anybody wants.

There could be a happy medium, where you have to get validated in-person that you are 18+ by a mutually trusted agency, and get an 18+ "badge", through some sort of trusted medium.

Plenty of legitimate, innocent, reasons to be getting an 18+ badge..and technically no real reason to record a persons information, except for anti-fraud measures.

I doubt there would be much more of a black market for that than there is already existing for getting nicotine and alcohol to kids. Shady people gonna shade. And of course, parents can slip one under their (teenage) kids pillow if they think they can be responsible with it.

Either way has a dystopian end...but that doesn't dismiss the value of having an "official" digital identity for "official" purposes (for whatever is deemed "official" by the holder).