I must admit that I've wondered about the structural integrity of ageing light aircraft for a while. How much of an airframe's original strength remains after forty years of use and exposure?
The thought has occurred to me that we'll only retire the current fleet of 60s/70s GA aircraft after a spate of horrific in-flight break ups. Metal eventually breaks after repeated loading and I can't imagine that owners will withdraw their machines from service 'prematurely'.
What bothers me slightly is that a fatal weakness would almost certainly be undetectable by a pre-flight visual inspection and possibly an annual check.