Prevalence-induced concept change describes a cognitive mechanism by which someone’s definition of a concept shifts as the prevalence of instances of that concept changes. The phenomenon has real-world implications because this sensitivity to environmental characteristics may lead to substantial biases in judgements. While prevalence-induced concept change has been established in young adults, it is unclear how it changes as a function of human ageing. In this cross-sectional study, we explore how prevalence-induced concept change affects older adults’ lower-level, perceptual, and higher-order, ethical, judgements. We find that older adults are less sensitive to prevalence-induced concept change than younger adults across domains. Using a combination of computational and experimental approaches, we demonstrate that these changes in judgements are sensitive to the pace with which the stimuli occur in the environment and are affected by the effort that subjects invest in order to make accurate decisions. Based on findings from three experiments we argue that older adults’ concept spaces are more rigid than those of younger adults. However, what appear as an age-related cognitive “deficit” may turn out to be beneficial because it makes older adults less susceptible to biases in judgments.