Privacy-Preserving Age Verification via Bank

I cannot buy anything on Steam which is marked as adult-only now even though I am an adult. There are a large number of adults who refuse to own a credit card or cannot own one. I personally cannot own one as I cannot work, so my income is not large enough to be accepted for one (I also do not want one). This form of verification is extremely flawed for this very reason, not every adult can be reasonably expected to own a credit card as not every adult can own a credit card. At this point, if I ever do want to buy an adult-only game, I will have to do exactly what kids can/will do: borrow my parents' credit card. There was a rather large outcry in the Steam discussions when it was first implemented with similar sentiment so I know I'm not alone with that. For any form of verification to work, it has to be something easily accessible to all adults while also not revealing too much or any identifiable information. (Simply having it an an option is fine, but having it as the only option just doesn't work.)