Earlier quoted context omitted.
Why should an OS demand personal information from its users? It creates an unnecessary risk that the information will be leaked.
Laws exist that dictate what apps are allowed to do depending on the user's age. This means that in order to follow the law they must collect the user's age. If collecting the user's age is a common requirement of apps it makes sense for the operating system to expose an easy way to do that to make app development easier on that platform.
User account creation wizards could just create the dot files for the App Store. These weird laws ban OS.