The sullen teenager grinding through a restaurant shift after school was once a pop culture cliche—as American as curly fries.

Nowadays, Brad Hamilton, the teen played by Judge Reinhold in “Fast Times at Ridgemont High,” would probably be too young to work at the fictional Captain Hook Fish and Chips. That’s because senior citizens are taking his place—donning polyester, flipping patties and taking orders. They’re showing up at casual dining chains such as Bob Evans and fast-food operators like McDonald’s Corp., which says it plans to make senior citizens one hiring focus in the coming year.

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