Comment by Jakob-G

But in reality this would not hide age, for example if a child signs up for Facebook, the only information revealed is that they are <16 years old. But once they turn 16, they want to have an unrestricted Facebook experience, so they will send a new token to Facebook, showing that they are older then 16 now. Facebook can now record the day the user does this and will now know the approximate birthday of a person. Sure, the user might not do this right on their birthday, probably in a span of a few weeks, but they will still have a good understanding of the age. This system would still be better then having to reveal your whole Id with all details.