Young Adult vs Adult Fiction – Why Not Both?

I just read this article that I think gives great insight into the art of writing for diverse age group audiences:

It’s interesting because as I get older, I tend to want to read novels that have characters closer to my age. That said, I will always love Harry Potter and The Chronicles of Narnia and a whole slew of other books that have children as the main characters.

I’m curious, what are your thoughts? Do you only read books with characters over (or under) a specific age?