The sequential flanker task was developed to study sequential performance using methodology borrowed from studies of task switching. We investigated age differences in backward inhibition [BI: Mayr, U., & Keele, S. W. (2000). Changing internal constraints on action: The role of backward inhibition. Journal of Experimental Psychology: General, 129, 4-26] during a sequential category search task. Participants learned four animal categories in a fixed order, and then searched for exemplars from those categories in runs of mis-ordered exemplars. Across three experiments, we observed robust BI facilitation effects. However, the magnitude of BI effects did not differ across age groups. This age-invariance held despite manipulations of distractibility (Experiment 2), and interstimulus interval (Experiment 3), suggesting that BI processes may be relatively automatic and obligatory in the context of sequential tasks. The findings are discussed in terms of the attentional mechanisms that underlie task set switching and sequential performance.