Age is a critical risk factor for severe COVID-19. This is mirrored by older people showing preventive health behaviors morefrequently. However, collective action across all age groups is necessary to reduce transmission. Therefore, this study assessed whether agedifferences are moderated by policy changes and whether policies further moderate the relationship between psychological determinants ofbehavior (risk perceptions and trust), age, and preventive behaviors. Risk perceptions, trust in institutions, self-reported frequency ofpreventive behaviors (mask-wearing, avoiding social gatherings), and demographics (e.g., age) were collected within the COVID-19 SnapshotMonitoring (COSMO), a German serial cross-sectional survey. A total of 19,069 participants across 20 measurement points were included(online sample, quota-representative for Age x Gender and federal state in Germany; mid-April to the end of November 2020). Regressionanalyses showed that age differences in avoiding social gatherings and mask-wearing remained stable under different health policies but werefurther moderated by psychological variables. The introduction of stricter policies alone was not related to higher adoption rates of preventivebehaviors, but it mitigated the effects of age and risk perceptions. Moreover, under mandatory policies, the correlation between trust ininstitutions and behaviors was amplified. The present research made a strong case for quality, targeted health, and risk communication.Without mandatory policies, the importance of preventive behaviors must be well understood to achieve high adherence–especially in youngpeople who are threatened by the disease less directly.