They already have the data and much more of it. This has nothing to do with “Big Corp” wanting to know how old their users are.
Something like https://protocol.humanidentity.io (disclaimer: I built it, sorry for the plug) or any other privacy preserving service might work better. A platform can then require that a person verifies age in a privacy preserving way before viewing adult content.
Or perhaps golfing at the right clubs to make it a defacto industry standard like ID.me seems poised to become?
I hate seeing stuff like this once and then never again due to people who are capable of making something this… Good being unable to “play the game” or whatever optimize to break the social-moral glass ceiling for a given problem space.