For the majority of turboprop a/c I have seen that are working for a living, the magic number seems to be about 2200 hours a year, with about forty minutes per cycle. There is of course wide variation, but that seems to be a fairly good average. The highest-time a/c I have worked on so far is a DC-3 with about 60 000 hours TTIS and it is still in service; I have also worked on a DC-3 with only 17 000 hours TTIS, while the fleet leader among DC-3s is up over 90 000 hrs TTIS.
An airframe will last for as long as it's owners are willing to spend money on it; several jetliners have reached 100 000 hrs TTIS. I believe that some of Northwest's DC-9s are the hardest-working a/c ever and are approaching 100 000 cycles.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.