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.