this is not going to just be a little file stored locally. The law says the operating system PROVIDER sends that signal to app devs. Think like they do and linux doesn't exist. You create an account for your phone already, whether Google or Apple. Just add the bday is a required field. Now it's across all your devices tied to that account. It cannot be changed once set. The idea is that parents buy the devices for their kids and will be asked to set the age for the child. Linux distros have no way to comply with this