Relative age, the differences in age between peers within a cohort, has been found to influence a variety of developmental outcomes (i.e., relative age effects). In sport, relatively older youth typically experience advantages, such as a greater likelihood of being selected to sports teams. Relative age effects have been repeatedly identified in a variety of sports, in athlete samples internationally, and in samples ranging from recreational youth participants to elite adult. However, this research, while important, has been described as somewhat atheoretical (Cobley et al., 2009). As such, we propose a theoretical framework that is evidenced-based and consistent with findings in this area. The foundation of this theoretical model is derived from Newell’s model of constraints (Newell, 1986) and the proposition that outcomes emerge from the interaction between individual constraints (related to the performer), task constraints (related to the demands and rules of the activity) and environmental constraints (related to physical and socio-cultural environmental characteristics). Our model also incorporates an epidemiological ‘causal pie’ structure (Rothman, 2002) wherein the specific salient constraints are depicted so that their size (‘pie piece’) is explicitly related to the magnitude of their influence on a RAE. This presentation will outline the evidence that supports the proposed model, and the model’s functional characteristics. In addition, we also present two methodological implications for future research that emerge from the proposed model: macro and micro studies of RAEs. Macro approaches are those that incorporate as broad of a systems-perspective as possible with a multivariate analyses of constraints (individual, task and environmental). Alternatively, micro approaches could test, perhaps even experimentally, the influence and mechanisms of specific constraints. Both approaches may have important implications for advancing this field and for future RAE interventions.