Stop Killing The Internet: No Digital ID & No Age Verification | European Citizens' Initiative
(citizens-initiative.europa.eu)
Honestly I think what is needed here is something similar to TLS: build a chain of trust with multiple "authorities" that can validate your age.
Then we can potentially have open identity issuers that validate age, minimum/no logging, ram servers, periodic power cycles, and independent audits. Assign the cert to an email address or something. Only include age >16/18/21 and a expiry date.
There would be a problem with tracking accounts across services, but if the cert name is only tied to an email, it wouldn't offer any more tracking info than the email used tied to your online accounts.