Is there any particular historic/socio-economic reason why the distribution of car ages at an auction site follows a bell curve? Just analyzed the image names of automobiles in an auto auction sale archive and filtered the image names by the automobile's model year and counted the years' frequencies. I came up with the following plot, which I found interesting and have decided to post here for your comments on what the reason for the spike is:

x-axis: time | y-axis:frequency of vehicles with that model year
 A: People can't sell a car manufactured in the future, so that accounts for the right-hand tail. Moreover, you're unlikely to sell a nearly-new car as an individual, so that accounts for the drop off. And you're unlikely to sell a car that is old/decrepit/at the end of its life due to maintenance costs and the general observation that a very old car is generally only useful for scrap. That accounts for everything left of the peak.
I don't know if this is a snapshot of a single-day's distribution of model years, but if this data is collected over time, it will be necessary to account for the fact that the model year of a car is fixed, and does not change relative to today's date. If you collected these data over a period of several years, you will also be reporting the fact that there are more opportunities for 2003 model year vehicles to appear: every year since 2002.
A: The "spike" or "bell-shaped curve" just means that intermediate model years, from 1995 to 2000, are more likely than extreme early or later model years.  Certainly, more cars will be sold from an intermediate period where they are no longer new but still usable, than from earlier periods when they are old and unusable (low demand), as well as later periods when they are still brand new and no need to sell them (low supply).
