That's a potentially reasonable argument, however there are a couple of issues mapping from the physical precedent to the digital world. In the physical world you would show your ID to the store clerk, or (more likely) not even be asked for ID at all if you were sufficiently old-looking.

In the digital world, everyone has to show proof of age, as there's no quick sanity check. Further, none of these states have a privacy preserving way of demonstrating age. All of them require either passing payment details or identity details to an intermediary or the website. The recipient of the identity then gets to hold onto whatever details you provided for the rest of time, and may use them for stuff like ad targeting. This is in an industry that is well-reputed for being scammy.