The average age of used cars in the United States has increased 14% in the last five years compared to 4% the five previous years. That's being caused by a variety of factors.

According to recent research from IHS Automotive (via the Wall Street Journal) "Vehicles on U.S. roads have never been older, now averaging 11.3 years. The average age of a vehicle will continue to increase over the next few years, but at a slower pace, rising to a forecasted 11.5 years through 2018."

The simplest factor in the aging of the American private passenger fleet of used cars would have to be dependability. Vehicles have longer shelf lives than they ever did in the past, in part because manufacturers are constantly trying to rein in warranty costs. Conquer those costs and companies become much more profitable.

What's it mean for you as a consumer? Both good and bad things in terms of price and availability.

In terms of price, wholesale used car prices are actually starting to rise in January 2014. That means supply must be tightening up a little bit as demand increases. Pent-up demand is a reflection of people putting off major purchases like a used car but finally needing to because they no longer have a choice. That must be playing a factor in the rise of wholesale prices at the start of 2014, which, in case you didn't know, is a bad thing for consumers.

Another bad thing for consumers is the longer used cars stay on the road, the longer they stay out of the used car marketplace.

People are no longer feeling the pressure to sell their used cars. Not that long ago it was common for people to sell their used cars once it hit five years or 75,000 miles. Holding on to them longer than that meant expected high repair costs.

Manheim Consulting has also determined that older used cars are not necessarily any less expensive. In its 2014 report on the used car industry, it determined (among other things), "We have looked at the average mileage on auction vehicles that sold between $4,000 and $6,000 over the past 14 years. As seen in the graphic below, if you spent, on average, $5,000 for a vehicle at auction in 2000, you got, on average, a vehicle with 84,541 miles.

"That average mileage slipped over the following three years as wholesale supplies grew and the overall pricing environment was weakened. But, since 2003, average mileage for the typical $5,000 auction purchase rose every year, except for the recession of 2008-2009. In 2013, the average $5,000 auction purchase had more than 120,000 miles."

What does this mean for you as a used car buyer and/or seller? Lets look at this from a seller's perspective first. The good news is you no longer have to consign your used car to the scrap heap (figuratively speaking) just because it has reached the 100,000-mile mark. With used cars having an average shelf life of 11.3 years, you can figure the average used car, assuming 15,000 miles of operation a year, will have almost 170,000 miles on it.

That means a used car with 100,000 miles on it is just shy of 60% of its expected life expectancy. So, a used car with 100,000 miles, assuming it has had decent maintenance for both its interior and exterior in that time, has a lot of miles left in it.

Also, older vehicles don't depreciate as quickly. That means you're not going to be penalized if you decide to hold onto your used car for another 10,000 miles to save some money. In the past there was pressure to sell a used car before the odometer turned over to six digits. Now it's just another milestone and not a huge financial penalty.

What does this mean for the used car buyer? Unfortunately the bargains are no longer automatically there on older used cars like they used to be. Especially now that new car dealers are seeing the value in selling older used cars.

That's not all bad news, though. Sure you are going to be paying more for your older used car, but you should also be able to get more life out of it. No longer is a used car with 100,000 miles on it something you could expect to wheeze along for a year or two. You can be comfortable thinking it will give you at least four more years (depending on how you drive) of service.

As always, especially when buying an older use car, insist on a pre-purchase vehicle inspection. Not all used cars are created equal and some are going to age more gracefully than others.