To evaluate a dual-task named the "Stroop Walking Task", which is similar to the task of making a decision of whether to cross a street based on a pedestrian traffic light. Fifty-one subjects (15 young adults, 21 subjectively healthy old subjects and 15 old subjects with mild cognitive impairment) had to respond to a visual signal (pictogram) with an appropriate motor response (walk or stop). We used an electronic walkway system to record the gait parameters and performed a cluster analysis on the obtained data. This dual-task enables the early detection of executive function impairment with 89% sensitivity and 87% specificity. The use of a dual-task that is inspired by an everyday event as an evaluation tool seems to facilitate the detection of ageing subjects' cognitive impairment, which is not detectable with traditional psychometric tests.