The Question and Answer section for O Pioneers is a great resource to ask questions, find answers, and discuss the novel.
We would be happy to help you with your questions. Please make sure your questions are detailed and post them separately.
Ivar is considered crazy cause he'd rather live surrounded by the animals he loves than people.
I don't think discrepancy is explained. As you alluded to, the author does not deal with ages of characters in any detail.