Convair 580s are still in use by Air Chathams for scheduled flights and those airframes date to no later than the mid-1950s..they also fly DC-3s on a charter basis, as does Buffalo Airways in Canada (until late last year Buffalo still had scheduled DC-3 service).

de Havilland Beaver/Otter and variants date from 1940s-1960s and are still in fairly widespread operation at least with charter companies and I wouldn't be surprised if there is a scheduled service somewhere.

Many light aircraft (Cessna, Piper, etc) are used in more remote areas on charter and sometimes scheduled service - a lot of those aircraft started production pre-1970 so while some may be newer, I'd imagine some older ones are still used commercially in those scenarios. Certainly they're still flown privately.