Niven is an uncommonly occurring given name for males but a very prominent surname for both adults and children (#19272 out of 150436, Top 13%). (2000 U.S. Census). Shown below is the baby name popularity of Niven for boys.
So, what length is the right one for a book? The average nonfiction book, if such a thing exists, runs about 50,000 to 75,000 words, but this can vary depending upon category. Biographies, for example, can run 200,000 words.
If you are insisting that on average a page is 500 words or 4,000 words the equivalent of 8 pages. By simple math you saying the average book is 80,000-120,000 words, would mean on average a novel is 160-240 pages. These would be classified as short novels or more so novels for older kids or younger teens.