26th Amendment

copied from: http://www.archives.gov/exhibits/charters/constitution_amendments_11-27.html

Passed by Congress March 23, 1971. Ratified July 1, 1971.
Note: Amendment 14, section 2, of the Constitution was modified by section 1 of the 26th amendment.
Section 1.
The right of citizens of the United States, who are eighteen years of age or older, to vote shall not be denied or abridged by the United States or by any State on account of age.

Section 2.
The Congress shall have power to enforce this article by appropriate legislation.

Any citizen at the age of 18 cannot be denied their right to vote. This amendment came about from President Nixon around the time of the Vietnam War where 18 year olds could be forced to serve in the military but had no rights to vote. The government could not tell the states how to hold their elections so in some states 18 year olds could vote, in others they couldn't. This amendment only applies for federal elections. 

 Being too young to vote but not too young to go to war....The government fixed it with the 26th Amendment.