tdracer said ..
90,000 hours is not that old for a 767 - even before I retired I was aware of several passenger 767s that had more than 100,000 hours and were still going strong.
One subtle reason for the very long fatigue life of the 767 and related was the extensive use of two Boeing devlopd processes. One being a technique called ' coldworking " details of which can be found in manuals, info provided by Fatigue Technology (
http://www.fatiguetech.com/ ) developed in the late 60's by Lou Champoux ( next to my desk ) at the time.. In simple terms, bypushing/pulling a mandrel thru a sleeve inserted in the hole - or a special mandrel without a sleeve, the hole stretches leaving the nearby surrounding material in tension, which then results in major fatigue improvement. This techniques was used on main spars, lower wing panels, parts of wing box and some parts of fuselage, etc.
The second process also ' first ' used on major spar assembly was/is called ElectroMagneticRiveting - which uses magnetic drivers to drive and expand a rivet in ONE blow, which also has a major effect on fatigue life. Although the process had been used on smaller parts/assemblies since early 747 days, the use on major spar assembly was a first on 767. The machine was known as ASAT automatic assembly tool. That also was the founding of a company used around the world as improved and further developed by a company called Electro Impact - whos major facility is next to Boeing Everett. They have branched out since then with major wing composite layup for 777X. And no - I do not and have not worked for ElectroImpact or Fatigue Technolocy but have had many personal contacts/background with those involved in both companies over the years.