In Article 1, Section 2 of the it states that the age for running for a seat in the United States House of Represenatives is currently 25. I believe that the age of 21 should be the age to run as those who are politically active at 21 should be able to run for a House seat.
Under Article 1, Section 3, the age to run for Senate is currently 30. This should be changed to the age of 25. This would allow both branches to get some new and fresh ideas into Congress and still have the maturity to help run the Legislative branch of the United States Government.