Don’t get me wrong, I’m all for privacy. But between setting up the birthdate when creating my children’s local account on their computers, and having to send a copy of their ID to every platform under the sun, I’d easily chose the former.
I’d even agree to a simple protocol (HTTP X-Over-18 / X-Over-21 headers?) to that.
The issue in general is that there is no organization that can be trusted to verify the age, but not find a way to leverage that into gathering some info about the child and selling it.
That aside. Age is mostly meaningless. Everyone matures at different rates. The difference in rate between girls and boys results in effectively several years meaningful difference. Like a 10 year old female muturity is more similar to a 13 years old boy than a 10 year old boy. And 18 is just an arbitrary number that happens to coincide with finishing high school. And has no actual association to maturity. This is why car rental places won’t rent to under 21s most of the time. Some hotels won’t let you have a room until 25. So trying to decide what content should be available based on age is pointless. And they know that. So they aren’t tryi g to protect anyone. They are trying to extract information they can sell.