It is a Boeing 737-200 and it has been in service for 43.7 years.
There are still DC-3's in commercial operation, and production of those ended in 1942.
http://www.buffaloairways.com/ is one operator.
Jets don’t like that.
For back country missions the only thing maybe better than a DC-3 is a Basler... and that is a modernized DC-3 with reinforcements and turboprops for more power. They suck a lot more fuel than a plain DC3 though, which can be problematic as some of these fields they have to fly fuel in.
Are there any such planes used for regular scheduled (passenger) airline services? It appears to me that Buffalo Airways is charter and cargo only.
Common definition of a "commercial operation" for airlines is scheduled operation, not charters.
So... That boeing just may be the oldest flying airliner on scheduled routes.