At what ages are young people most open to political influence? We test the "formative years" model that underscores the importance of childhood experiences for political development against the "impressionable years" model that asserts the primacy of lessons learned during adolescence. To assess the relative merits of these competing models, we develop a new analytical strategy: the Retrospective Family Context approach. We estimate the political engagement levels of 18-year-olds as a function of annual measures of their parents' political engagement levels over the course of the prior decade. German household panel data analysis shows that parental cues sink in quite effectively during late childhood, ages 9 to 11, and during the late teens. These results illuminate an essential dimension of political development, and they can inform efforts to encourage young people's political participation.