I was just reading some stats and they provided this chart:
Age 0-10yrs 5% of monthly income
10-25yrs 10% of monthly income
25+ 15-25% of monthly income
I would totally disregard anything you read from that source. Maintenance varies little due to the age of the house. It's true that you shouldn't have many capital expenses for a brand new house, but you'll very quickly begin to have other routine expenses such as carpet; paint; leaky faucets caused by tenants overtightening the knobs; clogged toilets; damaged appliances; frozen water lines when the tenant has their heat shut off; holes in walls; etc, etc, etc.
Even in the oldest properties, maintenance shouldn't be ANYWHERE NEAR 25%! In fact, any well maintained property, whether old or relatively new should have relatively equal maintenance expenses. I have properties from 175 years old to 6 years old and the maintenance is nearly identical.
Furthermore, capital expenses can occur in newer homes also. I bought a new home for my personal residence about 14-15 years ago and I've already replaced the heat pump twice and we're replacing the roof this year (due to storm damage). Yes, that's covered by insurance, but I have a $1,000 deductible. I have $5,000 deductibles on my rentals.
Mike