The issue of complexity is more and more present in numerous domains of biological research, including aging research. In the present paper, based on a selective review of literature, we propose both a conceptual and a methodological framework to address age-related changes in functional complexity of the neurobehavioral system, presumably resulting from modifications of the coupling between cognitive and sensorimotor processes. In particular, after reviewing pioneering and more recent studies on aging and complexity in the neuromusculoskeletal system, we explore the possibility that an age-induced increase in the coupling between cognitive and sensorimotor domains could be captured by a stronger covariation of high-order variables, common to both cognitive and sensorimotor functioning. Our main assumption is that these variables could behave as neurobehavioral markers of aging in the neuromusculoskeletal system. The present approach markedly differs from other traditional approaches, which focused on process-specific variable correlates of chronological age, domain-by-domain, and task-by-task. It provides a coherent conceptual framework, a terminology, and a method for studying age-related coupling of cognitive and sensorimotor processes with the use of complexity and nonlinear dynamical systems theories.