how long ago was the AN-2 designed?
A very long time ago...but they are still earning a living.
How long ago was the DC-3 designed....and yet some of them are still out there working today....perhaps most with Turbo Props now but the basic airframe design is the same.
The C-130 continues...as does the Chinook....and the Huey...sometimes a good design can find its niche in the market.