Preserving functional health and quality-of-life in old age is a major goal and global challenge in public health. The high rate of sedentary behavior that is characteristic of the older adult population exacerbates impairments of physiological and structural systems that are typically seen in the aging process. Achieving an understanding of the profound influence of physical activity on all aspects of health in old age is the driving force behind the emergence of "physical activity in old age" as a growing area of research. Accumulated evidence implies that being physically active and exercising is far superior to other optimal aging facilitators. Yet this area of research faces numerous constraints and obstacles. This commentary addresses some of these challenges, primarily the heterogeneity of the aging process, which induces both inter- and intra-individual differences among aged individuals, heterogeneity in assessment tools, unjustified inclusion/exclusion criteria and insufficient recruitment strategies, difficulties in implementing research results in real-world conditions, and rudimentary exploitation of innovative technology. We explain the importance of establishing a network of multidisciplinary scientists and stakeholders to propose consensus-based goals and scientifically evidenced wide-ranging plans for dealing with these challenges. In addition, we suggest work directions for this network.