You should paint interior walls every 5-8 years or whenever you want a different, updated, and fresh look to your interior aesthetic. Also, most homeowners paint before listing a home for sale or prior to moving into a new house.
Likewise, a new coat of paint can dramatically change the look of your home and results in an ROI of 107% when you are ready to sell. All things considered, interior painting is often a no-brainer for most savvy homeowners.