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.
The most reasonable choice now may not be the same forever. The optional indentifying fields themselves may have not have changed on Linux over the years but external changes in soceity has prompted this conversation.
With nefarious “child safety” laws popping up the introduction of an optional age field is tone-deaf and suspect. There are other objections to SystemD but this personally pushed me over the edge to finally try out another Linux distro (from Mint).