Of course various books have generic maturity levels. But all children are different, and so are all books; so general guidelines aren't always useful - I frequently encounter content that children theoretically aren't ready for yet, but greatly enjoy.
What are good guidelines to evaluate if your child is ready for a specific book's content?
NOTE: I don't care about the factor of being able to read the text - first, my kids reading level is well above their age, second I can read to them if the book is worth it but they struggle with more advanced text.
I already saw this question which seems like a duplicate, but whose answer addresses the opposite problem - is the child ready for the reading level of the book, as opposed to the content; AND doesn't really deal with specific child's capabilities. What I'm looking for is a process I can use to evaluate a specific book in terms of "is it too early to give to this specific child", not "is there a generic guideline that an average 3rd grader would understand 80% of the book".