This topic is something near and dear to my heart. I have a confession...I am a grown adult man and I still love to read YA fiction! Phew, I'm so glad to get that off of my chest.
Growing up in a small town reading books that were considered "young adult" or "graphic novels" didn't really exist. Every bit of the young adult and graphic novels were located within the adult section. Granted, this was about 10 years ago. Nowadays there are specific sections for both in many libraries. Before moving to Dallas, I worked at the Carmel Clay Public Library in the Young Adult Services Department. During the day there obviously wasn't much teen traffic as they were at school, so much of my interactions before 3:15pm were with adults. Believe me, adults LOVE young adult books. The question wasn't about whether or not adults like young adult/graphic novels, but how can we as librarians work to make sure they feel welcome in the section and that they have as much ownership to these books as teen patrons. I believe working in teen services has helped me gain some knowledge with these ideas.
One of the very first things that I did to try and entice adult readers and support their claims that YA books were legitimate choices were to partner with the Adult Services department. Each month there is a staff spotlight that showcases some of our favorite books to read. Rather than sticking to solely "adult" titles, I added some young adult books into the mix. There were bookmarks that went along with the displays so adults were able to see that the books were located in the Young Adult section and by giving them a chance to pick up the book from there, they in theory would have a chance to browse the full collection. This may seem simple, but I noticed a few adults with my bookmark starting to peruse the collection.
Another way that I have tried to make to highlight the teen and graphic novel collection to adults so that they feel like they are able to read the collection is to create displays in the teen section as well as make sure patrons are signed up for the monthly "suggested reads" newsletter that sends out books based on their likes to the patrons. These "suggested reads" include young adult books and graphic novels. I like to also point out to patrons that we have a vast downloadable collection that they are able to check out from the comfort of their home, including ebooks, audiobooks, and graphic novels (through hoopla).
For me, it is an absolute necessity for us as librarians to ensure that adult readers who enjoy graphic novels and fiction feel as though they can pick up any of the books. Every reader is different and because of that, it is our jobs to make sure that even adults feel welcome to read books that may be deemed "too young/immature" for them. The Young Adult section has evolved over the years and many of the books involve hard hitting situations that are often times more complex that many would think. Just because the section in the library has a title of "Young Adult" or "Graphic Novel" that doesn't mean that those books are limited to that population of readers. The library is an open space for all and because of that librarians need to make sure everyone feels welcome to read whatever they want when they want.