The authors studied the effects of aging on the flexible use of categorization rules based on thematic and taxonomic relations. Two components of flexibility were distinguished: maintenance of a categorical relation, and switching between two relations. Results showed that age affects these two components. In older adults, an effect of the nature of the categorical relations to be used was revealed. Older adults demonstrated a specific difficulty in the flexible use of taxonomic relations. Moreover, all adults, independent of their age, showed better performance in maintaining the use of a categorical relation than in switching between two categorical relations.