This study examined whether the proposed bilingual advantage in inhibitory control and working memory can be extended to a trilingual advantage, and assessed any age-related effects on a continuum in young adults to older adults. Trilinguals, bilinguals and monolinguals' performance on the Simon task and a numerical version of the N-back task was compared. On the Simon task, there was no language group difference observed, although the data show an age-related decline in inhibitory control only in trilinguals, but not in bilinguals or monolinguals. No clear language group differences were observed between trilinguals and bilinguals on the N-back task, however an overall trilingual and bilingual disadvantage, compared to monolinguals, was observed. Together the results suggest that managing two or three languages, compared to just one, may have a negative impact on inhibitory control and working memory performance. Importantly, they highlight the need to control for a possible confounding effect of including trilinguals/multilinguals in bilingual cohorts and to ensure that participants in monolingual cohorts speak only one language.