Then create one, or something much better than is being demanded, first; before demanding companies use it.

If a porn company has to collect all the information about me (name, address, age, etc) and keep it in their database then, if they get hacked, then all that information, connected to what I viewed, is available to the hackers.

If the porn company has an ID that it assigns each person, and it reaches out to some government agency to say "is this person of age" (without their internal ID), then stores "yes/no" with the ID; then hacking cannot (or is much less likely to be able to) connect "what account has viewed what" with "what human being is attached to the account".

Effectively, by making the porn site need to collect and maintain personal information, privacy is made less safe. If the government is going to demand proof of age, then the government is on the hook for supplying a reasonable way to check it.

Then create one, or something much better than is being demanded, first; before demanding companies use it.

Before demanding car companies build safer vehicles I first invented the seat belt.