Accumulating evidence has suggested that older adults display a weaker correspondence between their retrospective confidence judgment and actual memory accuracy than younger adults, suggesting age-related declines in metamemory. However, the underlying mechanism for such age differences remains an open question. The primary goal of the study was revealing to what extent age-differences in verbatim- and gist-related memory processes could explain the age differences in metamemory accuracy. In this study, the verbatim and gist features of DRM word lists were factorially manipulated during encoding. Younger and older adults completed three consecutive free recall tests after encoding, and rated confidence for their recall accuracy. Fuzzy-trace theory’s dual-retrieval model was used to estimate the two verbatim-related retrieval processes (direct verbatim access and forgetting) and two gist-related retrieval processes (reconstruction and familiarity judgments). The results show that metamemory accuracy was predicted by direct verbatim access, reconstruction and familiarity judgment at individual level for both younger and older adults. However, only direct access mediated the effects of age on metamemory accuracy, while other processes did not. This suggests that age-related decline in metamemory depends heavily on age-related difference in verbatim memory.