The ALA's position as posted on their website is that there is no such thing as "age appropriate" material. They believe that if it is in the library, all patrons should be able to access it.
This doesn't mean to them avoiding stocking something like Madonna's Sex book or an "X" rated film like Last Tango In Paris, instead it means requiring parents to restrict their kids card (since by default the ability is there) so that they cannot check out ANY videos without parental approval. Not sure how the library wants books "limited" in access since no arbiter reviews books. There is a "code" for comics, but the x-rated works of Robert Crumb (which do have some valid content) carry no CCA code.
With the culture here, there are no x-rated videos in the video section and no books like the "Joy of Sex." When I worked in a library, that was the book that I found most commonly out of place.
That being said, it amazes me sometimes what parents will let their kids watch, even in a very conservative community such as mine.