This paper uses discontinuities imposed by voting-age restrictions to identify the effect of past eligibility on subsequent participation decisions and partisan identification. It compares participation decisions and partisan affiliations of individuals who turned 18 just before past elections with those who turned 18 just after. It presents three main findings. First, past presidential election eligibility increases the probability of subsequent participation. For example, the point estimates indicate that 2000 presidential election eligibility increased participation in the 2004 presidential election by 3.0–4.5 percent, which suggests that voting in the 2000 presidential election increased 2004 participation by about 5 percentage points. Second, past presidential election eligibility affects partisan identification. Third, these effects continue to persist for several election cycles after a voter first becomes eligible.