Not really an age-issue or design issue. The investigation showed that MacAir/nee "Boeing" built the fuselage longerons incorrectly (too small; not to design specs). This issue did not affect the E-model.

What I don't understand: Why couldn't the Air Force make Boeing liable for their mistake, and fix it?

The total cost estimated to repair the 150-ish jets affected was $500k each, or about $75 million. The Air Force instead opted to retire those airplanes, saying it "....wasn't cost-effective."

Instead, they advocated vigorously (and lost) an argument to replace those 150 jets with additional F-22s.

BTW: the cost to repair those jets? Half the price of ONE F-22. Smart move.

There is also no guarantee that the F-22 doesn't have a ticking bomb in it like this. Oh wait, OBOGS......