Identifying the difference in the barriers and motivators between middle-aged and older adults could contribute toward the development of age-specific health promotion interventions. The aim of this review was to synthesize the literature on the barriers and motivators for physical activity in middle-aged (50–64 years) and older (65–70 years) adults. This review examined qualitative and quantitative studies using the theoretical domain framework as the guiding theory. The search generated 9,400 results from seven databases, and 55 articles meeting the inclusion criteria were included. The results indicate that the barriers are comparable across the two age groups, with environmental factors and resources being the most commonly identified barriers. In older adults, social influences, reinforcement, and assistance in managing change were the most identified motivators. In middle-aged adults, goal-setting, the belief that an activity will be beneficial, and social influences were identified as the most important motivators. These findings can be used by professionals to encourage engagement with and adherence to physical activity.