The Edmund’s calculator works for six year old vehicles and newer. The AAA calculator is for three year old cars and newer. It won’t work for a ten year old vehicle, but can give the OP an idea of how different vehicles compare to each other. It is likely that if a six year old car costs 20% less to operate over 5 years than a different one, then that 20% likely holds for a ten year old vehicle.
I like the Edmunds True Cost to Own feature too for making purchasing decisions. I think I’d add something to the six year old car estimates for repairs since failures are much more likely in a 10+ year old vehicle.
Another possibility is to take the last two years of the six year old car estimate (car age 10 and 11 years) annd average them.