When using Mass-Sell Aircraft feature, the age of the aircraft goes up significantly with each step in the process. I just listed some 3.3 year old aircraft, by the end of the process, it shows them being 7.7 years old. The aircraft get listed for sale with the correct age, the problem is only on the Mass-Sell Aircraft pages.
This happens regardless of game world, and presumably user (mine is 52188). I've seen this occur every time I've used this feature.