Drawing on social exchange theory, our study aims to examine how age-inclusive human resource (HR) practices affect work engagement by shaping the age-diversity climate and perceived organizational support (POS). We hypothesize that diversity beliefs play a moderating role in the relationship between age-inclusive HR practices and POS. Our analysis of a sample of 983 employees from 48 organizations in China highlights the direct impact of age-inclusive HR practices on work engagement. Moreover, age-diversity climate and POS mediate the association between age-inclusive HR practices and work engagement. We further demonstrate that diversity beliefs play a moderating role in the association between age-inclusive HR practices and POS. Our findings not only contribute to the literature but also provide practical implications for managing an aging workforce.