A call for opposing arguments: Why should the age of candidacy not be lowered to 18 years of age?

What arguments can you make against lowering the minimum age of candidacy for Congress to 18 years of age?  Arguments should be structured with premises, inferences, and a conclusion (loose structure is okay as long as the premises can be clearly identified).  Let's try to keep this an intelligent conversation and do this with as much credibility as possible.  If you have not already read the argument for lowering the minimum age then follow this link to read up on it: http://www.change.org/petitions/united-states-congress-lower-the-minimum-age-for-candidacy