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.
I could imagine a parental control setup using this information, for example. Linux is really behind in this regard and it’s time it started catching up IMO.