> Someone over 18 person could indeed decide to help others prove age, but they would either have to do it in person or be willing to loan their unlocked security element to those others.

You can still automate age-verification-as-a-service using a physical autoclicker on a smartphone with the camera oriented at a screen showing QR codes. I expect this to happen, and for that reason I also expect true anonymity to be something that will last a year or so until it will be politically decided to fix the issue using some central party that verifiers have to contact to impose rate limiting.