To address the challenges imposed by demographic change, organizations have become increasingly interested in maintaining and improving employees’ work ability across the working life span. Based on signaling and social exchange theories, we present a study that investigates the indirect influence of age inclusive human resource practices (AIHRP) on work ability through age diversity climate (ADC). Using a 6-wave longitudinal study of $n$ = 355 employees, we model between- and within-person mediated effects using a random intercept cross-lagged panel model. The results of this analysis partially support our mediation hypothesis. Specifically, we found evidence that ADC mediates the influence of AIHRP on work ability at the between-, but not at the within-person level of analysis. These findings have implications for the development of human resource practices that benefit employees at various ages.