The results provide a better understanding of age-related changes in risk and protective factors of alcohol use across the transition to adulthood. Impulsive personality traits are stable risk factors for alcohol outcomes until the late-20s despite typical age-related declines in these traits and drinking. Moreover, parental monitoring buffers the association between personality traits and alcohol harm for specific youth during the transition to adulthood. Personality-targeted interventions may be effective beyond adolescence, and parenting interventions may help reduce harm among low perseverance, low sensation-seeking youth.