This study is devoted to the analysis of institutional corridors of transition to adulthood in Russia during the twentieth and early twenty-first centuries, with a focus on how demographic waves, state policies, and historical events shaped the timing and sequence of initial life course events. The theoretical framework draws on the life-course perspective, M. W. Riley’s concept of age stratification, and contemporary demographic research. Data from the Russian Longitudinal Monitoring Survey (RLMS) for 2003 and 2023 show that institutional changes in education, employment, and family and demographic policy created distinct institutional pathways that structured the timing and order of educational, labour-market, and matrimonial events. Methodologically, the study combines an analysis of Russia’s demographic structure in 2023, an institutional-historical review of education, labour, and family policies over the past century, and a comparison of the socio-economic and demographic conditions under which cohorts born between 1930 and 2009 entered adulthood. The findings indicate that demographic waves and institutional transformations shape the “corridors” of life trajectories by influencing the likelihood of key adulthood transitions. In post-Soviet Russia, the mismatch between biographical trajectories and institutional norms has intensified, resulting in more prolonged and variable transitions to adulthood. The study shows that the models of growing up among contemporary Russians are shaped by the interplay of demographic dynamics, institutional inertia, and political decisions. A clear trend toward the destandardization of the rigid “education–work–marriage” sequence and the extension of “biographical youth” is observed among post-Soviet cohorts.