Originally Posted by
tdracer
Perhaps, someday, the high time aircraft will be one of those new-fangled carbon fiber 787s or A350s - carbon fiber doesn't fatigue the way aluminum does. But it'll be a couple decades before that can possibly happen.
My understanding is that it's not the airframe itself that is the principal reason for retirement (and it not having any operational secondhand value), but all the fittings, the wiring especially, the control runs, the need for cabin refreshes, the IFE becoming outmoded, etc. This becomes cumulative over many of these items as time passes, and progressively impacts on dispatch reliability. It particularly applies where some of the hundreds of initial suppliers of these smaller components have gone out of business over the years, and spares and support for them becomes increasingly expensive or difficult.