What are the best rated used cars
Consumer Reports does articles like that. Research this site and other automotive sites for the type of car you want and look at the good reviews.
Good to look at many sites not just one. But you gotta decide what type of car your looking for, cause one car might get great ratings and then when you test drive it you don't like it. Just got to look around and not buy the first car you see. Look for promotions too
If you're meaning old as in with over 100,000 miles for a teenager or college student then you best stick with Toyota and Honda