Older adults often report memories of past events that are partly false. To date, age differences in memory errors have primarily been examined after a delay of minutes to hours. However, in real-life situations we rely on memories formed days to weeks in the past. We examined associative memory for unrelated scene-word pairs in younger and older adults after 24 hr and 8 days. Age differences in memory were magnified after 8 days due to a disproportionate increase in false alarms to rearranged pairs in older adults. In both age groups, the effects of delay were modulated by memory fidelity and whether or not participants had experienced similar events, which potentially caused interference. Older adults were particularly vulnerable to associative memory errors having experienced similar events, even when the initial memory was of high fidelity. We suggest that the fidelity of memory representations in concert with monitoring processes to resolve interference determine how the passage of time affects the propensity to falsely remember details of the past.