@sjmulder You are probably not wrong, it is a very stupid law. but by my reading the OS only had to provide the age, an application may have to verify it. And the law does not say anything about when an application has to verify anything. so that never needs to be done.
My conclusion after reading it was that on a unix like system compliance may be as simple as
echo $AGE_CATAGORY > ~/.config/ca_ab_1043
It is an accessible user interface, applications can use a well established API to get the data, it shares as little as possible.
But really, it is such a stupid law that it smells of a frog boiling scheme to me, that is "lets see if we can get the OS vendors to do something easy now, for more intrusive tracking later... For the children of course."