How would that work in practice? A lot of us here operate websites. Your website gets a request. How are you supposed to tell the age of the person that request came from? Maybe Google / Facebook have enough data to identify the person and their age, but ironically, they would have to collect information about them to determine that it's a person they shouldn't collect information about.
Certainly no child in the history of the Internet has ever lied to a website when asked their age.