I really think it depends on the conditions the vehicle is run for. I did an UOA on my 1996 Contour using PP 5W-30 run for almost 8,800 miles over 18 months or slightly more. It was a mixture of highway and "local", almost no stop and go, driving. Wear metals were low and the TBN was 3.5, plenty of life left in the oil after ~8,800 miles and over 18 months of use. As stated here previously, oil does not know time only how it's used. My BIL bought a used Porsche Boxster, 5 years old with 9,000 miles on it with the factory fill. He did a UOA on the FF and it came back with not bad wear metals and plenty of life left in the oil. This Porsche was a "fun" vehicle used only in nice weather conditions and warmed up totally before garaging again. I'd be more concerned with the type of use, does the oil get hot, up to temp when it's used vs short trips where the oil never gets hot.
Whimsey