Maintenance cost of 50 years plus property?

[Stanley H.]

I was reading Mark Ferguson's blog and came across this cash flow calculator.

http://investfourmore.com/rental-property-cash-flo...

In that he mentions that house older than 50 years have on an average 25% maintenance cost. Is this an accurate representation?

I am asking this because that reduces my future cash flow assumption considerably.

Let me know your thoughts

Thanks