PurposeTo examine the relationship between country-level age norms for sexual initiation timing and early sexual initiation (ESI) among adolescent boys and girls. MethodsNationally representative data from 17 countries that participated in the 2006/2007 European Social Survey (ESS-3, n = 33,092) and the 2005/2006 Health Behaviour in School-Aged Children Study (HBSC, n = 27,702) were analyzed. Age norms were measured as the average country-level response to an item asking the age at which ESS respondents believed someone is too young to have sexual intercourse. HBSC respondents (aged 14–16 years) self-reported age at sexual initiation, which we defined as early (<15 years) or not early (≥15 years or no initiation). Control variables included age, family affluence, perceived socioeconomic status, family living arrangement, substance use, school attachment, and country-level legal age of consent. Multivariable three-level logistic models with random intercepts were run separately by sex. ResultsIn multivariable analyses, higher overall age norms were associated with reduced likelihood of ESI among girls (AOR .60, 95% CI .45–.79); associations with ESI were stronger for parent cohort (ages 31–65 years) norms (AOR .37, 95% CI .23–.58) than for peer cohort (ages 15–20 years) norms (AOR .60, 95% CI .49–.74). For boys, overall norms were also significantly negatively associated with ESI (AOR .68, 95% CI .46–.99), as were parent cohort norms (AOR .66, 95% CI .45–.96). Peer cohort norms were not significantly related to boys' ESI. ConclusionMacrolevel cultural norms may impact adolescents' sexual initiation timing. Research exploring the sexual health outcomes of early initiators in countries with contrasting age norms is warranted.