Previous research has shown that bilingual children perform better than comparable monolinguals on tasks requiring control of attention to inhibit misleading information. The present paper reports a series of studies that traces this processing difference into adulthood and eventually aging. The task used in all groups, from children to older adults, is the Simon task, a measure of stimulus-response incompatibility. The results showed that bilinguals performed better than monolinguals in early childhood, adulthood, and later adulthood. There was no difference in performance between monolinguals and bilinguals who were young adults, specifically university undergraduates. Our interpretation is that performance is at its peak efficiency for that group and bilingualism offers no further boost. The results are discussed in terms of the effect of bilingualism on control of attention and inhibition through the lifespan.