Why for the most part old people served in the white as leader of this nation?

why we dont change the constitution and let serving young intelligent individuals who would a fresh front to this nation. We only have old half death people that for the most they hate their life a want to past laws to make the rest of the nation suffer. for example mr. chenney who knows how many open hearth surgeries he has been thru. Bush had some type of cancer and so on and on, etc.....