The question is, is HE interested? Being from Minnesota, my son had to read one of the books and watch the videos of the old 1970s tv series and learn about the Ingall's-Wilder family as part of a school assignment.
Apparently, he and his (guy) buddies were far from interested in the books and only cared about the pioneers after they had to spend the day at an historic one room school house like Mrs. Ingalls Wilder attended and later taught at, and then later got to learn about the westward expansion, Jesse James' last stand in Northfield and the Civil War.
I think for the boys, it wasn't until they got to see real cannons getting fired off, getting to see real guns and pictures of the bank where the James robbery took place, and learning about the gore of war surgery methods of the pre-technological age at the local historic fort that he had any interest in state history, let alone the pioneers.
I think he thought the books didn't focus enough on the things boys care about, and alot on the experiences of a young girl on the prairie and later a young woman finding her way in life as a teacher, wife and mother. So I think this is why he didn't care for the books.
This of course is based what he has told me. Your son may like them. I guess try showing him the tv series on video (though they are not much like the books) and see if he's interested in reading about that time in history and take it from there.