What model was that? Some manufacturers put time limits on such hardware. American Champion, for instance, recooomends replacement of main landing gear U-bolts (or their replacement, the clamp bar NAS bolts) at 500 hours. If an owner ignores these recommendations, he might find out why they're there.
Stationary bolts such as those that attach the wings and tail are fine if they're properly torqued and the airplane hasn't been overstressed in some way. Bolts that act as pivots wear out and should be replaced when worn. And I have often replaced bolts that I found way overtorqued, such as engine mount and brake caliper bolts. Too many mechanics think that if tight is good, tighter is better. They risk failed hardware and an accident.
Corrosion is a much bigger failure factor than fatigue, I think.