> If you are in this articles audience you would simply state the producer of the ID card signs a statement that the person is over 18. No ZKP needed.

> The article like many others would be improved with a better example.

It's easy to make this example better:

Assume there are 50 different providers of ID cards, and Alice wants to convince Bob that she's over 18 years old.

Bob trusts all 50 issuers, but Alice doesn't want to reveal who her issuer is.

So here Alice could indeed get the supplier of her ID card to sign such a statement (and perhaps already have one prepared). For ZKP, you can also assume that the ID card issuers are not co-operating (nor do they care about each other), and that different Bobs might trust different sets of providers, and that the sets of trusted providers might change over time.