Final answer:
The 26th Amendment gave all males over 21 the right to vote.
Step-by-step explanation:
The amendment that gave all males over 21 the right to vote is the 26th Amendment.
The passage of this amendment was a result of the youth activism during the Vietnam War, as many argued that if people were old enough to be drafted into the military, they should also be old enough to vote.
The 26th Amendment was ratified in 1971 and it lowered the voting age from 21 to 18, ensuring that 18-year-old males had the right to vote.
Learn more about Voting rights for males over 21