Maybe someone like apple will make a "verify user looks over 18" neural net model they can run in the secure enclave of iphones, which sends some kind of "age verified by apple" token to websites without disclosing your identity outside your own device?
Having said that, I bet such a mechanism will prove easy to fake (if only by pointing the phone at grandad), and therefore be disallowed by governments in short order in favour of something that doesn't protect the user as much.
Apple lets you add IDs to your wallet in some jurisdictions. I wouldn't be surprised if they eventually introduce a system-wide age verification service and let developers piggyback on it with safe, privacy-preserving assertions.