It is well known that working memory performance changes with age. Two recent computational models of working memory TBRS * and SOB‐CS , developed from young adults WM performances are opposed regarding the postulated causes of forgetting , namely time‐based decay and interference for TBRS * and SOB‐CS , respectively. In the present study, these models are applied on a set of complex span of the main parameters of these models showed that the poorer performance of older adults does not come from a weaker encoding of item but rather from difficulties during the free time that immediately follows each distractor , as well as from a higher level of confusion between items. These results are discussed with respect to the current theories of working memory and aging.