How often should walls be washed?

I want to help my Pops out and I offered to wash all of the walls down at his house. It’s been five years since my Mom died and the house needs a good cleaning. I keep up with washing baseboard, but, not the walls. Most of the rooms were painted 5 years ago (two years before Mom died), and so, that’s my Dad’s thinking. It’s only been 5 years and that there is no need. My siblings disagree and feel that they could use a good washing.

I have no problem doing it. Just wondered what you all think. How often do you wash down your walls? Do you really think that it’s neccessary after 5 years.

My Dad is not the cleanest individual. His idea of clean is putting stuff away. I think that I’ve seen him wash a floor, maybe, twice since my Mom passed and I’ve never seen him dust. Usually, I’m the one over there giving the house a good cleaning.

I’m just curious and would love to hear from you all..

This may seem like a silly question, but, I don’t have all of the time in the world and I’m wondering if I should even bother. It’s a bigass house and there are a lot of rooms/walls to be washed.