Since starting this thread and identifying, via Post #4, the oldest KC I've scoured FR24 looking for elderly airframes. Last night I struck gold and found KC135 s/n 57-1440 stooging about at 12,000ft over The Wash, I know it's all in a day's routine for the crews but I find it quite remarkable that a 62 year old airframe is still out there on the front line doing it's bit. The fact this 62 year old girl is still delivering is testament to the "rightness" of the original Boeing 367-80/707 design. I wonder if we'll ever see 62 year KC 46/767's? I rather think the KC135 is the jet equivalent of the DC3 in that it will see off every contender for its replacement.
