I'm not following. Depreciation is largely based on age, so the older the car, the better the deal. Conversely, wearing out is based largely on miles rather than age. So an old car with low mileage is going to be cheapest per mile you get out of it.
Instead of a 3yo Honda with 90k, an 8 yo Honda with 60k will cost less in purchase price and yet you will get more miles out of it. Much lower cost per mile you get from it. Lets say either car is going to die at 200k miles. Car 1 costs more and only gets you 110k miles. Car 2 costs significantly less to purchase and yet gives you $140k miles. How can that not be a better deal?
OP mentioned having about $9,000 which puts a purchaser in the range of a newer old car as long as you stay in the economy segment. Using the example of a base Honda Fit, and getting private-party values from truecar for one with a manual transmission, I get the following:
2012 with 24,000 miles: $11,459 (out of reach)
2012 with 100,000 miles: $9,336 ($2,123 cheaper, and almost in reach)
2011 with 36,000 miles: $8,649 (in budget)
2011 with 72,000 miles: $6,985 ($1,664 cheaper. This is twice the average mileage and seems to be a sweet spot)
2011 with 100,000 miles: $6,967 ($1,682 cheaper, though interestingly truecar gives the same value for a 2011 with 112,000 miles)
etc.
Note that as the car gets older and the average mileage increases, the purchase-price savings of the higher-mileage car diminishes. As I mentioned in the post you quoted, this approach only pencils for relatively new cars (4 years old is probably too much).
Granted, I'm assuming mustachian levels of driving (say 5,000 miles/year). Since the OP is wondering about whether to drive an older car I'm assuming (I know....) some hesitation about reliability, etc. Buying the higher-mileage 2012 Fit means OP can buy a 3-year old car instead of an older one. Newer cars also tend to have more sophisticated safety features and get better mileage.
At 5,000 miles a year it takes 20 years to drive 100,000 miles. I've never owned a car 20 years--my record is 13.5 years and the most I've put on a car is 155,000 miles (my miles, not necessarily the odometer reading). All the others were either wrecked (not my fault, and really glad it wasn't a 15-year-old car in that accident), needed a repair more expensive than what I was willing to spend, or were sold off due to a shift in functionality requirements (larger family). I can't guess what kind of car I'll need in 20 years, so I don't plan on keeping them that long. Also, as I've noted elsewhere, a lot of car parts start failing at around 10-13 years old, regardless of mileage.
So, if I buy a 3-year-old Honda fit that has 100,000 miles on it, in ten years (when it will start experiencing problems with little systems based on age alone), I can sell a 13-year-old car with only 150,000 miles on it.
Clearly, this is not going to pencil for everyone. I guess I'm arguing that a lot of people buy a used car with unused miles they will never use; why pay for those miles?
I have a sort of gut feeling that the value sweet spot in age for price/fuel economy/safety is probably from 3-13 years, perhaps 5-10 years. I also prefer to avoid driving super old vehicles and, since I like driving, appreciate a little variety over time. YMMV.