What airplane designs have been around the longest, from first flight through last retirement from active commercial or military service?
My guess is that the DC-3 will win, since it has been around since before WW II and is still in service, although there are enough other designs out there I'm not familiar with that I'll be interested to see where I may be wrong on that. (Russian designs come to mind as an obvious source of possibilities.)
Can anything out there beat the DC-3? What's the runner up?
(The wikipedia page on the DC-3 says its first flight was December 17, 1935.)