I think I probably did not understand the actual definition of mistress. But, I understood the book. I was an advanced reader. By the time I was 10, my teacher was searching for books that I could read for class. Yes, I did read all of the usual, Nancy Drew, Hardy Boys, Trixie Belden, Little House etc. However, I enjoyed the classics early. Particularly, Poe.
That’s the nice thing about those books. Good authors can communicate their ideas without getting terribly clinical. The story works on both levels. My daughter was able to read Pride and Prejudice after 8 but before she was versed on what houses of ill repute were. So she could read it without real problems. Bleak House can’t quite pull it off because of the central theme of the whole thing, though Dickens is certainly in the same class, and was a bit of a social revolutionary in some ways himself (”Hard Times”). I get the feeling that Dickens was a bit apolitical regarding parties, though, and had a genuine love for England with her warts, and all.