This article focuses on the social construction of age relationships in businesses, through an approach based on their management devices (organization and division of labor, human resource management, financial management). These devices are not implemented to handle or regulate the question of ages or intra- or inter-generational relationships, rather that of qualifications, production, and financial earnings. Nevertheless, they have an indirect influence on the age relationships at work and the professional models in which they take place. From two business monographs, the article shows that the expression of management devices in each organization creates particular configurations of age relationships. Both cases highlight that management devices help professionally define age, making it relative. They attribute positions and offer careers differentiated according to age or the time of entering employment. Therefore, by creating particular configurations, they help build specific and variable age relationships according to the organization. In this way, age relationships, far from being pure institutional products, must also be considered the result of local and specific organizational forms, anchored more generally in the ways of organizing, framing and assessing work.