I can see this argument, but it has a few caveats:
- The 'faucet', providing infinite key material in an open proxy is also very vulnerable
- If the only attribute is age verification then uniqueness is not required; i.e. you can borrow the key of someone you trust and that should be fine.
- The unlinkability is a requirement from the law itself, i.e. the current implementation cannot be executed upon assuming rule of law holds