The only way this can be implemented at the OS level (not the vendor level) is to put in whatever date you want. That includes any notion of scanning “IDs”.
If you want to setup a kid’s account on a phone or pc, then you have the control. If they are smart enough to do it themselves, then hey- don’t hold them back.
My immediate concern is giving sites additional fingerprinting material. The OS better not give away an actual birthdate- when they can option for adult/not-adult, etc. Next concern is moving the age verification to a corporation, at which point the dystopia is real.
This isn’t even malicious compliance. It’s just compliance. The owner of the system can set ages for system users. Smart people will set it to what they want.