If we go back a few years and analyze the porn magazines that are sold in a gas station, it's not up to the magazine to ensure that the "reader" has the legal age.

So we delegated the responsibility twice, first the gas station attendant must check the age of the buyer and then, the buyer should check the age of any reader.

So now, who's the "gas station attendant" in our situation?

because there are other sites/apps online too, and it's better to decouple the "obtaining the verification" and the "presenting the verification"

and if sites and apps don't need to be in the loop for this they can't end up leaking all over the 'net