You've likely seen photos of airplane graveyards. You certainly have if you've read the blog before. These graveyards On the other hand, you've probably also looked out your window while taxing to or from a terminal before and seen - off the in distance at the Cargo terminals - a beat-up 747 that has to be at least thirty years old. What's with the disparity?
This is one of those things that isn't obvious, until you hear it, and then makes total sense: airplane age is not a function of time, but a function of pressurizations. This is rust-resistnt metal. Existing doesn't wear it out very quick. Neither does shooting through cold, thin air. Instead, being inflated and deflated over and over like a balloon is what causes the stress, both on the metal skin and the things that hold that metal to the frame and the other metal.
Planes flying short haul (think: NY/DC) have very short lives, taking perhaps 3-5 pressurizations a day. That 747 you saw? It might take 3-5 presurizations a week, so it can last, theoretically, over 50 times longer.