Developmental scholars, parents, and policymakers alike have long heralded the opening years of life as disproportionately influential. Recent work on adolescence has revealed, however, greater influence of these later years--but without considering how experience during these two periods interact. We address this issue by studying adverse experiences (e.g., parental divorce, incarceration) measured at ages 0-5 years and 13-18 years on problematic development at 18-19 years (e.g., criminal behavior, disconnection from school and work) on 363,444 Danish siblings. Given multiple possible interaction patterns, no predictions were advanced. The extent to which adverse experiences in early childhood impact future problematic development depends on level of adversity experienced in adolescence: Only when exposure to adversity in adolescence was limited did greater early life adversity predict poorer future outcomes. Otherwise, adolescent adversity swamped effects of early life adversity. Results are discussed in terms of the design and context of the research.