Age-induced paranoia

At what age does the mind step over the line between a touch of madness to fully cracked? Or can it always be a sign of an unglued mind? Perhaps it is simple frustration that mistakes are being made and time is limited.

At the grocery store an elderly woman exhaustively explains that the pie she has purchased is mislabelled and this is her second attempt to remedy the situation. She tells the cashier it is not a cherry pie, but rather a fruit pie. After calling the manager as per her request she continues her diatribe about the inconvenience of taking numerous buses just because of this mistaken pie incident. After the manager approaches she then takes it to another level, proclaiming that because this is the second time this has happened to her, all of the pies are mislabelled and surely the result of a person's "sick joke".