This is a great book for anyone to read. Based on my child I would say 14/15 and up, but it is a know-your-child sort of situation. Some children may not be mature enough to read something like this at that age.
This is a difficult, heavy read. Incest, rape, torture, murder, as well as adult emotional themes are included. As said in the title, this book is historically accurate of that era - this is what people, specifically African Americans, went through during that time. We should not censor our children from the pain of the past. It is important for them to know what life was like, and what the true harm of slavery really is.
I would recommend reading this with your child and discussing it in a book club setting. It is easy for a younger teen, or even an adult, to miss some of the crucial themes (motherhood, redemption, etc.).