In the United States as of 2014, candidates for Congress must be 25 years old to run for a seat in the House of Representatives and 30 years old to run for a seat in the Senate. Other countries have other age minimums for their respective legislative bodies.
At the time when the U.S. Constitution was being written, the English Parliament had an age restriction of 21 years on politicians serving within its halls. Inspired by this, the framers of the Constitution placed age restrictions on those serving within the House and Senate. The Senate has a higher age minimum than the House because the framers of the Constitution envisioned the Senate as providing more stability and deliberation than the House.