To qualify to vote in the United States, one must be at least 18 years old and a U.S. citizen. In many states, committing a felony or being found mentally incompetent can disqualify one from being allowed to vote.
Over time, the right to vote has expanded in the United States. Until the passage of the 26th Amendment to the Constitution, the voting age in the United States was 21. In 1920, the 19th Amendment guaranteed women the right to vote. Following the Civil War, which ended in 1865, the 15th Amendment extended voting rights to men of all races, rather than just white men.