My guess is that androgen sensitivity increase with age, and therefore inflammation and scalp mechanical stress result of it
Yes. Hamilton has already proven the same amount of androgens cause much faster hair loss in older men than younger ones. This is why propecia loses effectiveness over time. Its not ARs changing its simply whatever causes sensitivity keeps increasing to overpower the propecia.
Also I think male pattern baldness is going to be found similar to allergies someday where some men immune system attack hair because of DHT while others do not. Its an immune reaction at its core that differs between men for unknown reasons. Why do some people have allergies but not others? Its the same basic question