This is the American Library Association’s stance as well. They hold that there is no such thing as “age appropriate material”. That said they also believe that all content (that passes their political litmus test) should have shelf space in the library.
I’ve never heard of a library official or staffer being prosecuted for corrupting a minor for providing access to adults only materials.
The ALA’s position is that if you want to limit the access of your child (say no access to R, NC-17, X and yes there are X “art films” in some library collections, or unrated videos, no Robert Crumb underground comix, no Joy Of Sex, no...) then YOU should not permit your child to have a library card and should restrict his or her access to the library itself (since items do not need to be checked out in order to be accessed and a card is only needed to remove an item).