The predictive value of the Theory of Planned Behavior (TPB) on intention and physical activity (PA) over time was examined. Data from the Aging Well and Healthily intervention program (targeting perceived behavioral control and attitude, not subjective norm) were analyzed, including pretest (T0), posttest (T1, except subjective norm) and 4-6 months follow-up (T2, PA outcomes only) (N = 387, M age 72 yrs). Structural equation modelling was used to test a TPB model. PA was measured subjectively using the Voorrips sports subscale (T0 and T2), items measuring perceived increase in PA (T1), and adherence to exercises (T1 and T2). Model fit was good. TPB explained variation in intention well (R2 0.54 to 0.60) and some of PA behavior (R2 0.13 to 0.16). The intervention successfully got participants to exercise independent of the measured TPB concepts. More TPB studies in the context of interventions are needed.