Introduction Cognitive-motor interference increases with age during dual-tasks, especially with visual/spatial cognitive tasks. We posit that visually and physically exploring a novel environment may constitute a dual-task for older adults (OA). Given known associations between gait modifications and structural brain alterations, we also consider whether a potential dual-task cost in this setting could be linked to age-related brain atrophy. Material and methods Fourteen young and 14OA had to find an invisible goal in a real, ecological environment; their body and eye movements were recorded. We calculated walking speed, trajectory efficiency (direct route over the route taken) and fixation ratio (fixations directed outside the goal area over fixations toward the goal). Dual-task cost was calculated for walking speed (DTCS) and learning indices (LI) for all three variables. 18 of these participants (10young, 8older) realized a MRI voxel-based morphometry evaluation. We performed a correlation analysis between DTCS and grey matter volume. Results OA showed increased DTCS upon first exposure. The LI on walking speed correlated positively with those on trajectory efficiency and fixation ratio, likely indicating an alleviation of resource-sharing between walking and encoding the environment. DTCS correlated negatively with GM volume in the superior parietal area, precuneus and superior occipital gyrus. Discussion-conclusion We interpret OAs' larger DTCS as indicative of cognitive-motor interference. This is supported by the correlations between the LIs and between DTCS and GM volume, especially considering that these brain regions are involved in visual attention and sensory integration. Our findings under ecological conditions question what constitutes dual-tasking in OA.