While a growing body of literature is concerned with researching the opportunities, risks, and consequences of lowering the voting age, extant research has neglected the side-effects of an uncoordinated implementation within federal systems. Voting age reductions tend to be implemented in lower-level elections first. If, for instance, a state election with voting age 16 takes place less than two years before a national election with voting age 18, some underage voters eligible for the former will have no right to vote in the latter. Analyzing a panel survey of young citizens from Germany, we find that under-age voters who were eligible in a state election in May 2017 experienced a decrease in external efficacy and satisfaction with democracy after not being eligible to vote in the national election five months later. Even after regaining eligibility in another subsequent election, the net effect of temporary disenfranchisement on external efficacy remains negative.