Some of the DC9-14s are probably vintage 1965 or 1966......There are probably some vintage 1966 or 1967 DC9-30s as well....
You have to remember that a majority of these DC9s came from the amalgamation of three basic airlines North Central, Southern Airways and Hughes Airwest. Hughes Airwest itself was made up of three carriers: Bonanza, Pacific and West Coast.
Southern's DC9-14s mostly came as ex-Eastern and Ex-Delta DC9-14s as those carriers phased them out. N948L if its still flying around is a former Bonanza DC9-15. The 30 series are mostly ex-North Central, Delta, Hughes Airwest, Eastern, N994Z is even a former Ozark bird.
An Interesting story about N994Z is that one time whilst doing a flight for Ozark, it had landed in Sioux Falls, SD
and hit a snow plow on the runway, and the plow knocked one of the wings off. The plow driver was killed in the accident. However the insurance company had the aircraft fixed and it was subsequently sold to Republic airlines, where it now flies for NW
The oldest DC9-30s are undoubtedly North Central birds and they might even have a couple Ex-Northeast Airlines 30 series. The 50s (built between 1975 and 1980 or so) are ex-North Central for the most part altho a few former Eastern DC9-50s have crept into the fleet. One of the NW
DC9-50s I have flown on was N600TR which was actually a former Venezuelan airliner. A couple of 30s are from JAT of the former Yugoslavia one of which is N926RC. The 40s were picked up as SAS had decided to dump them out of their fleet.
The DC9 is a remarkable bird and as Ozark used to call them..."The Bugless Douglas."
The days are prolly numbered sadly but it goes to show you that they don't make planes like they used to. I'm thinking the reason that NW
has kept them this long is because they have two engines and have a two man crew. Had they been like the 727s, they would have been Looooooooong gone!!
I hope that helps some...