As a result of demographic changes, workforces are becoming older and more age diverse. While interactions between workers from different age groups can provide opportunities for mutual learning through bidirectional knowledge transfer, research has yet to investigate how age influences knowledge transfer between age-diverse colleagues. Building on the organizational theory of age effects, we conducted two studies to examine how age influenced the roles assigned to individuals in knowledge transfer processes, that is, whether they were perceived as knowledge senders or knowledge recipients. In Study 1, we used an experimental vignette design with 450 employees to assess how age affected perceived ability and motivation to share and receive knowledge. Further, we tested the extent to which trustworthiness moderated these relationships. In Study 2, we extended these findings using a dyadic research design with data from 53 age-diverse knowledge transfer dyads. We examined through which mechanisms the age of one's colleague affected one's knowledge transfer behaviour. We found that the age of one's colleague had a positive effect on one's knowledge receiving behaviour and a negative effect on one's knowledge sharing behaviour. Further, perceived ability to receive knowledge and perceived motivation to share knowledge mediated these effects.