"The older he gets, the less he understands."
Translation:Jo eldre han blir, jo mindre forstår han.
Why does the location of han differ for blir (before) compared with forstår (after)?
It is the jo. I don't know why, but the base form is jo - comparative - pronoun - verb, jo - comparative - verb - pronoun.
Comparative/parallell sentences are made with jo - jo, jo - dess, jo - desto, dess - dess, dess - desto. They seem more or less interchangeable.