While much of the literature on bilingualism and cognition focuses on group comparisons (monolinguals vs bilinguals or language learners vs controls), here we examine the potential differential effects of intensive language learning on subjects with distinct language experiences and demographic profiles. Using an individual differences approach, we assessed attentional performance from 105 university-educated Gaelic learners aged 21–85. Participants were tested before and after beginner, elementary, and intermediate courses using tasks measuring i.) sustained attention, ii.) inhibition, and iii.) attention switching. We examined the relationship between attentional performance and Gaelic level, previous language experience, gender, and age. Gaelic level predicted attention switching performance: those in higher levels initially outperformed lower levels, however lower levels improved the most. Age also predicted performance: as age increased attention switching decreased. Nevertheless, age did not interact with session for any attentional measure, thus the impact of language learning on cognition was detectable across the lifespan.