Aims: Unlike adults, abstaining has increased and regular use of alcohol has decreased among 12–16-year-olds over the past two decades. The paper studies whether these developments will be continued as the adolescent cohorts come of age. Methods: The Adolescent Health and Lifestyle Survey is a nationally representative monitoring system of the health habits of 12-, 14-, 16-, and 18-year-old Finns, conducted biannually between 1981 and 2013. The prevalence of alcohol use and drunkenness were measured for each 5-year cohort born in 1967–1995. Age-by-cohort trajectories and hierarchical age–period–cohort (APC) modeling were used to assess effects of age, period, and birth cohort. Results: Cohorts differentiate for underage drinking, but not at the age of 18. The younger cohorts postpone their drinking debut compared with older cohorts and thus age profiles are steeper than before. The most recent cohorts born in the 1990s, and the oldest cohorts born in 1967–71, have the highest prevalence in abstinence but drinking has been more prevalent for cohorts born in 1973–1989. APC modeling confirms significant cohort effects, but no significant decrease in drinking or drunkenness at the age of 18 years. Some of the changes can also be attributed to period effects. Conclusions: Despite the decrease in underage drinking in Finland, 18-year-olds continue to drink similarly from cohort to another. Postponing the onset of drinking has a preventive effect on alcohol-related harms, but a reduction in drinking among adult cohorts is not evident in the future.