You might say that someone is a stereotypical person or that he fits the stereotype. A stereotype is a generalized (often oversimplified) idea or expectation for what a certain group of people are like. If a person fits the stereotype, they fillfill that idea or image exactly. You could also say, "He is a person who thinks in stereotypes." Then you mean that his ideas about people are very generalized or oversimplified. He has very strong expectations that everyone he sees will fit into a mold.