As global aging accelerates, the prevalence of mild cognitive impairment (MCI) continues to rise, highlighting the need for ecologically valid cognitive-motor rehabilitation technologies that can enhance users’ motivation, adherence, and training intensity. In this study, we developed a mixed reality (MR) supermarket shopping system that leverages head-mounted and hand-tracking sensors to capture users’ cognitive and motor performance in realistic daily activities, such as price calculation and beverage preparation. Fifteen older and twenty young adults (older adults: 54–65 years; young adults: 19–21 years) participated in 30 min MR-based shopping tasks using a Meta Quest 3 headset. System usability, workload, sense of presence, game experience, simulator sickness, and physiological responses were evaluated. Results showed that both age groups rated the system as usable and enjoyable, with no significant difference in overall usability or enjoyment score. The young participants reported higher physical workload, whereas the older adults rated the interface quality higher, suggesting age-friendly accessibility. Minor visual fatigue was reported without severe cybersickness. The older adults demonstrated lower speed but maintained over 80% task completion and perceived the system as beneficial and motivating. These findings support the feasibility of sensor-enabled MR systems across age groups, indicating strong potential for use in cognitive-motor rehabilitation and the early detection of age-related functional decline.