Especially on the local level, the age for candidacy for elected office should be no greater than 18. In some small municipalities, mayors and city council members are in their teens. At state and federal levels, ages should remain in the mid-20s or higher simply because those jobs are more complex and constituencies are larger.
Every state and local gov't is different, but most don't specify any particular age for office. The Federal Government has age limits of 25 for the House of Representatives, 30 for the Senate, and 35 for the Presidency. This seems reasonable to me, although I could see an argument for lowering the Senate requirement to match the House of Representatives requirement.