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.
You’re a bit behind the times. adduser has been asking for your full name since the dawn of Unix.
Edit: and if you don’t put in your full name, how will people know who they’re fingering?!