The cognitive consequences of multilingual language experience remain a topic of considerable debate. Much of the existing work has focused on executive functions (EF), yet the impacts of multilingualism may also extend to the broader cognitive domain, and they may be subject to changes across the lifespan. In this study, we examined whether degree of language balance was associated with performance in EF and fluid intelligence across adulthood, and whether such associations are more apparent in periods of age-related cognitive change. Participants were 117 young adults and 115 healthy aging adults. Language dominance was measured through self-reporting and L2 vocabulary tests, whereas cognitive assessment included the Stroop task (EF) and WAIS-IV subtests (fluid intelligence). Across analyses, greater language balance showed only weak protective effects against age-related cognitive decline, which did not remain reliable once age and education were included in the models. In the younger adult group, no links between language balance and cognition were observed at all, whereas in the healthy aging group, which represents a period of increased cognitive vulnerability, only minimal and inconsistent patterns emerged. These findings suggest that the cognitive effects of multilingual experience as measured by language dominance in healthy adults are limited and strongly overshadowed by age and educational background, indicating that such effects may be more fragile than previously assumed.