Once a person turns 18 years old, he or she can vote.  This right was granted by the 26th Amendment to the Constitution in 1971.  The 26th Amendment was brought about because at that time, the voting age was 21and many Americans under the age of 21 were being drafted into the military to fight in the Vietnam War.  Many people argued that if someone was old enough to fight and die for their country, they are old enough to vote.