What term describes a bias against people based on their age?

The term that best describes a bias against people based on their age is prejudice. Prejudice specifically refers to preconceived opinions or feelings, often negative, directed toward individuals or groups based on characteristics such as age. In this context, it implies a judgment made about someone solely due to their age, without considering their individual merits or behaviors.

Discrimination refers to the unfair treatment of individuals based on visible characteristics, such as age, but is more about actions rather than beliefs or attitudes. Bias is a generalized inclination toward or against something, but does not specifically capture the negative connotation associated with judgments based on age. Stereotyping involves oversimplified and fixed ideas about people based on their age, which can lead to prejudice, but it describes the generalizations rather than the bias itself. Therefore, prejudice is the term that most accurately encompasses the unfair attitudes towards people based on their age.