What do you mean, he “admitted” that?
It’s quite literally the first thing he wrote in his pull request to systemd:
Stores the user's birth date for age verification, as required by recent laws
in California (AB-1043), Colorado (SB26-051), Brazil (Lei 15.211/2025), etc.
And the second paragraph of his pull request to arch:
Recent age verification laws in California (AB-1043), Colorado (SB26-051), Brazil (Lei 15.211/2025), etc. require platforms to verify user age. Collecting birth date at install time ensures Arch Linux is compliant with these regulations.