We tested how the bilingual processing system adapts to high attentional processing loads, using a dual selective attention task. We also tested how this adaptation changes with maturation, by comparing the performance of monolingual and bilingual children and adults. Results showed equivalent performance on aspects of the dual attention task (auditory comprehension and visual task accuracy) for monolinguals and bilinguals in both age groups. Reaction times from the visual task however revealed differences between groups, with bilingual children’s responses significantly slower relative to monolingual children under high processing load, but the bilingual adults’ performance equivalent to their monolingual counterparts. The results suggest that the adaptation of bilingual selective attention changes with maturation: high attentional processing demands lead to economising of the available attentional capacity and task prioritisation in children, but these effects recede as the attentional system fully matures, resulting in consistent optimal performance across elements of multiple tasks in bilinguals.