How old do citizens have to be to vote for President?

Citizens must be at least eighteen years old to vote for President in the United States. This age requirement is established by the 26th Amendment to the U.S. Constitution, which was ratified in 1971. The amendment ensures that citizens who are eighteen or older cannot be denied the right to vote based solely on their age, reflecting the belief that individuals of this age have reached a level of maturity and responsibility appropriate for participating in the democratic process.

The other age options provided (sixteen, twenty-one, and twenty-five years old) do not align with the legal requirements for voting in federal elections. Sixteen-year-olds are not permitted to vote as they are still considered minors and not fully independent. Twenty-one was the previous voting age for several decades before the 26th Amendment was enacted, and twenty-five is not a relevant age restriction for voting in federal elections. Thus, the correct answer emphasizes the contemporary voting age of eighteen years as mandated by constitutional law.