This study examined the influence of verbal self-instructions on age differences in task switching. Task-switching ability, measured as the difference between performance in single-task blocks and in mixed-task blocks in which participants switch between two tasks (mixing costs), increases during childhood and decreases in old age. To measure the influence of language on task switching, we compared conditions in which participants either (a) named the next task to be performed (i.e. task-relevant verbalization), (b) verbalized words not related to the task at hand (i.e. task-irrelevant verbalization), or (c) did not verbalize (control condition). Results indicated that mixing costs were substantially reduced under task-relevant verbalization and increased under task-irrelevant verbalization. Moreover, age-related differences in mixing costs were increased when the use of inner speech was disrupted and were reduced when participants performed task-relevant verbalization. These findings suggest that verbal self-instructions are a useful tool for retrieving the next task goal and for reducing action-control deficits in younger children and older adults.