Google has to do this to comply with COPPA. They had to pay a $200m fine in '19 due to users that weren't age-checked.
I'm no lawyer and can't say whether Google complied in a minimal fashion or not. But maybe not. [Edit: Checkboxes are insufficient, apparently]
But apparently Google's knowing that you're a right-handed tae-kwon-do enthusiast that flies every month is not sufficient for them to maybe think you're not a minor.
FWIW, I'm always happy to give my dob to these websites. Its the epoch of course. Memorable for me and boring for them.
(as they should)