Bob Dylan had an album called "My Back Pages". I've also seen the expression in
other contexts. Being from Sweden, I'm curious about the origin and meaning of this idiom - if it indeed is an idiom?
Not sure, but here's a try:
"back pages" is used to describe the news that is printed in the last part of the newspaper, on the back pages. It is less important than the front page news. Could be the detailed, less exciting part of his life that he used for music inspriration.