With the accelerated aging of the global population, uncovering the social decision-making mechanisms of the elderly becomes increasingly crucial. Prior research has rarely focused on age-related differences in reciprocal behavior, and empirical research into reciprocity behavior within the context of trust remains sparse. The present study employs three laboratory experiments to investigate differences in trust reciprocity behavior between younger and older adults, illuminating its underlying psychological mechanisms. The results revealed that: (1) Upon receiving trust, older adults exhibited higher levels of trust reciprocity behaviors than younger adults. (2) Interpersonal responsibility completely mediated the age-related differences in trust reciprocity behavior. (3) The moderating effect of reputational concern was marginally significant, such that younger adults were more sensitive to reputational information and demonstrated more trust reciprocity behaviors under the reputation condition, whereas older adults were less influenced by reputation, showing no significant difference in their proportion of choosing trust reciprocity behaviors regardless of the presence or absence of reputational information. These findings extend the scope of the age-related positivity effect and provide theoretical support for fostering an active aging society

trust reciprocity, age-related differences, interpersonal responsibility, reputational concern