For those interested on the question of age verification and GNU/Linux: be aware that Systemd v261-rc1 was recently released. It now implements an optional birth date field in the JSON user database (see second item under “Other changes”).
The implementation of this field was prompted by age-verification or -attestation laws.
It’s not up to the systemd team to decide for you what your risk tolerance is. They’re just providing a means to be compliant should you want/need it.