Humans, as prosocial animals, expose themselves to the risk of exploitation if they fail to determine whether other individuals are trustworthy. People are keen to ascertain the trustworthiness of others that they instantly form initial impressions of others’ trustworthiness from perceptual cues, especially from faces. However, because perceived trustworthiness has low predictive validity, “true” trustworthiness of another individual must be learned from that person’s actual behavior. Considering the increasing societal and scholarly attention to fraud victimization among older adults, we conducted a series of studies comparing the perceptions and learning of other people’s trustworthiness between older and younger adults. The results showed a cross-age similarity in trustworthiness perception (Study 1), but an age-related decline in trustworthiness learning (Study 2). Furthermore, ventral striatal activity was found to be related to older adults’ failure to learn trustworthiness, suggesting the involvement of motivational mechanisms (Study 3).