My bnose catfish male, Dyson is the oldest resident of my tank. The others in the 30gal are relatively new (due to a disaster I had with the tank in January)....I have had Dyson since December 2003.
Other long surviving fish are my cichlids which I have had since March 2004. They have never been sick with anything. No ich, no finrot, no suicides, no deaths AT ALL.