It should definitely not be an enabled by default thing that’s for sure. I think when you’re setting up your system, you should get the option to enable birthdate. Then allow restricting access to specific things based on birthdate.

At no point should that control be passed on to anyone beyond the system administrator though. This could be useful for schools and homes with kids that you want to give user accounts to while maintaining a single age filtered list of applications. There’s no reason for it to be included in anything beyond that though.