Which is more than the law requires. What they’re supposed to report is an age bracket. You don’t need to store someone’s precise date of birth, and you certainly don’t need to make it available to other software, to report a broad age bracket

Optional as far as systemd is concerned, perhaps, but it’s designed to support a whole suite of software which will expect it to be used.

They’re also making dubious decisions about how it will be done, such as how they’ll handle the fact that date of birth is PII and something advertisers will be delighted to know. The laws they’re trying to support require very limited information, but they’re storing far more than that and they’ve actively decided not to protect it properly.

However optional it may be, they’re effectively defining the standard for what will be stored and how it will be accessed by all of the software which will use it