Young adults are underrepresented in American politics, but political scientists have devoted little attention to age bias in political participation and public policy. Drawing on arguments that groups vary in their cohesiveness, and that groups with stronger shared identity participate in politics at higher rates, we explore the relationship between age identity and political participation. Using data from a survey of a nationally-representative sample of adults, we measure how strongly citizens identify with others in their age group. We find that young adults do tend to have weaker age identity than senior citizens, but also that their average age identity is as strong as their political party identity. Second, we explore whether age identity is associated with two forms of political participation: voting and participating in protests related to climate change. We find that age identity is a strong predictor of both forms of political participation, especially for young adults.