The right answer is twenty five years old.

In the United States, a person must be at least 35 to be President or Vice President, 30 to be a Senator, or 25 to be a Representative, as specified in the U.S. Constitution. Also, most states in the U.S. have age requirements for the offices of Governor, State Senator, and State Representative.

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Specifically, Article I, Section 2 of the Constitution sets three qualifications for representatives. Each representative must: (1) be at least twenty-five years old; (2) have been a citizen of the United States for the past seven years; and (3) be (at the time of the election) an inhabitant of the state they represent. Members are not required to live in the district they represent, but many of them traditionally do.

The age and citizenship qualifications for representatives are less than those for senators. The constitutional requirements of Article I, Section 2 for election to Congress are the maximum requirements that can be imposed on a candidate. Therefore, Article I, Section 5, which permits the House to be the judge of the qualifications of its own members. But, it does not permit the House to establish any additional qualifications beyond the Constitution. Likewise no state in America can establish any additional qualifications for House members.

More Info: en.wikipedia.org