The automated attack setup I'm envisioning is something like:
18 year old buys a cheapo laptop + phone and connects the two over ADB or some purpose built automation app (think appium). 18 year old puts the phone on a tripod pointed at the laptop screen.
14 year olds at school pay $10 a year for use of the service and install a browser extension that forwards the QR codes from whichever service they wanna use to the 18 year old's computer. Changing every couple of seconds is not an issue here, they all live in the same city and have <10ms ping.
The only high friction part of this is that someone needs to write the software for it, but that doesn't seem like all that difficult of a project and open source solutions are likely to appear within weeks of social media requiring it. If there really is no information shared with the other party beyond "yup, user is over the age of maturity" you could even run this as a free public TOR service without fear of ever getting caught.
Mhh, but then the Danish Agency for Digitisation will see that the 18 year old does a lot of age request on all day and night long. And block his account. And then he can't use his own banking, health, postal apps.
High risk, low reward.
If he throttles request to stay under a threshold, if the agency knows about it service they could use it and see which account does age requests at the same time.
Ah, so it does leak your identity through the timing side channel. In other words, your anonymity is only dependent on the govt not coordinating with service providers to de-anonymize users. I assumed the 2fa app just held cryptographic keys and did some 0kp magic to show that the cert belongs to a government-attested adult. Phoning home all the time makes it trivial for the government to abuse people's privacy; they can just compel service providers to provide logs of logins.
Well right now THAT service does not even exist. The SSO exist, the anonymous age verification was an idea from another user here. Instead of sending (face)data to a private 3rd party.
The only high friction part of this is that someone needs to write the software for it, but that doesn't seem like all that difficult of a project and open source solutions are likely to appear within weeks of social media requiring it. If there really is no information shared with the other party beyond "yup, user is over the age of maturity" you could even run this as a free public TOR service without fear of ever getting caught.