Yes, picture books for older readers are definitely a thing, though, you're more likely to find them in the educational market rather than trade. Capstone does these. My book For the Right to Learn: Malala Yousafzai's Story is geared to grades 4 and up due to its content (a child activist who survives an assassination attempt). My avatar is also a pb for older readers done through Capstone/Smithsonian.