It's a tough balancing act.
Realistically it depends on how many miles you do a year.
Generally you could argue that a car is economically good for around 15 years or around 200K miles, depending of course on how it's treated. Anyone with a bit more mechanical knowledge (and is prepared to do a bit of work on it themselves) should be able to get more from it.
Let's use an example. If someone drives about 10,000 miles a year, and they're looking for a car, and there's two main choices for the price, a 2009 with 150,000 miles, and a 2005 with 70,000 miles. The 2005 car would have five years of use left (assuming a 15 year lifespan) and the 2009 would have five years as well (assuming a useful life of 200,000 miles). At that point, it's probably line ball, although the 2009 vehicle is likely to be a generation newer with all of the advancements that brings.
However, if that same person only drives 5,000 miles a year, the equation swings in the favour of the newer, higher mile vehicle. If they drive 25,000 miles a year, then it goes the other way.
In my case, I bought a 2002 late last year with 111000km (69K miles) on it, even though I do about 11000km (7K miles) a year. Whatever, for the price range I was looking at I was eyeing stuff made between 1998 and 2005, with anything up to about 250,000km.
Oh yeah, make sure the thing's been serviced! Skipping scheduled services is likely to shorten the car's lifespan.