Physical activity is a crucial determinant of overall health and well-being, significantly influencing both physical and mental health outcomes. Understanding the intricate patterns of physical activity across different age groups and health conditions is essential for developing targeted interventions. Mental health conditions like depression and schizophrenia are known to affect physical activity levels, yet the extent of this impact across age groups remains under-explored. This study uses a complex network approach to investigate the influence of age and mental health conditions on physical activity patterns. We analyzed the relationship between physical activity and age in individuals with depression and schizophrenia, comparing these patterns with those in healthy individuals. Specifically, the study examines whether physical activity decreases with age and explores the correlations between physical activity levels and health status.