This inquiry explored whether lifelong bilingualism can be associated with increased executive control, especially mental flexibility, and with a modulation of an age-linked decay in these functions. It compared performance of middle-aged and elderly speakers of German and bilingual speakers of Dutch and Frisian in a cued task-switching paradigm. All bilinguals were fluent in the same, closely-linked language pairs. Bilinguals incurred significantly lower switching costs than monolinguals, and elderly bilinguals were less influenced by an age-linked raise in switching costs than monolinguals. Bilinguals did not diverge from monolinguals in the size of the mixing costs. The findings propose that lifelong bilingualism correlates with increased skill to shift between mental sets, as well as raised resistance to proactive interference. The fact that significant group differences were found– while some prior studies did not – may be imputable to the choice of this task and to the cognateness of the languages involved.