Reading age is a crucial metric in children's literature that indicates the age range for which a book's content is suitable. It's based on vocabulary, sentence structure, and themes presented within the book. For instance, a book with a reading age of 5-7 years is tailored for early readers, employing simpler language and concepts. This helps parents, educators, and librarians select appropriate materials that align with a child's reading capabilities, promoting better literacy development and engagement with literature.