Although decades of research show the health benefits of regular exercise in older adults, the affective mechanisms underlying these benefits remain poorly understood. In fact, research on exercise-induced affect has generally lacked a clear framework for explaining how specific exercise features influence emotional experiences in older adults. This theoretical paper addresses this critical gap by proposing the circumplex model of affect as a comprehensive approach to understanding how exercise modifies valence (pleasure–displeasure) and arousal (activation–deactivation) in older adults. Using interdisciplinary evidence, we explore how neurobiological mechanisms (e.g., BDNF-mediated neuroplasticity and oxidative stress regulation) and hormonal pathways may differently affect affective valence and arousal, the two main dimensions of the circumplex model, during aging. We also explore how key exercise variables, such as intensity, type, duration, and frequency, are linked to distinct affective profiles within the circumplex model, and how individual differences in cognition, health, and socioeconomic status influence these relationships. Our review of the literature reveals that heavy reliance on one-dimensional mood measures has masked important differences between emotional quality and activation level. We argue that using the circumplex approach allows for a clearer understanding of exercise affect links and moves the field beyond the vague claim that exercise improves mood. This circumplex theoretical framework could provide a stronger foundation for developing targeted, evidence-based exercise interventions to improve affective outcomes alongside physical health benefits in older adults.