Historically, women, racial minorities, and the working class were excluded from voting on the basis of their supposedly insufficient political maturity. Nowadays, the same argument is used by opponents of enfranchising 16-year-olds. However, recent research suggests that voting can influence citizens’ subsequent attitudes and behaviours, so their political maturity may depend on whether they can vote. Does enfranchisement affect citizens’ political maturity? I address this question by leveraging a quasi-experiment in Germany, where states enfranchised 16-year-olds at different times, starting in 1996. The results show that enfranchising 16-year-olds can equalise prior differences in political maturity between underage and adult youth – measured by their political interest, efficacy, willingness to vote, and attitudinal consistency. This effect appears to be driven by an increase in demand for political information amongst the newly enfranchised. The findings suggest that 16-year-olds should not be excluded from voting on the basis of insufficient political maturity.