This study theorizes and tests moderators (perceived availability of marijuana and age-group) of the association between adolescents’ frequency of marijuana ad exposure and past-year marijuana use. To test this model, I analyzed national survey data from 9,024 American adolescents with hierarchical regression techniques. Results showed that being a male (95% confidence interval [CI] for unstandardized regression coefficient [0.06, 0.16]) and peer pressure (95% CI [0.04, 0.14]) were positively associated with past-year marijuana use, and father education (95% CI [−0.11, −0.06]) was negatively associated with it. Perceived ease of access (95% CI [0.18, 0.22]), ad exposure (95% CI [0.03, 0.14]), and age (95% CI [0.16, 0.27]) were positively associated with past-year marijuana use. Importantly, the associations of perceived ease of access and age with past-year marijuana use were significantly larger than that of ad exposure. Age (95% CI [0.00, 0.15]) and perceived ease of access (95% CI [0.01, 0.07]) independently strengthened the ad exposure to use association. There was a significant three-way interaction (95% CI [0.01, 0.12]) showing that age increases the positive influence of perceived ease of access on the marijuana ad exposure to past-year marijuana use association. An exploratory analysis further revealed that male adolescents are more strongly influenced by perceived ease of access compared to females. Based on the findings, I suggest that approaches for reducing perceived marijuana availability and for implementing age-specific interventions are promising avenues for prevention programs aimed at decreasing marijuana use in adolescents.