Ignoring the fact most of the electorate don't know the issues at any given time the principle of voting at 18 is important, if you know your politics at 14 then you have had 4 years to develop a context for the politics of the day and will make a more informed decision, those that were jerks when they were 14 may have developed a slight understanding of issues. Basically the problem boils down to this, citizens are those that contribute to the process through taxes, engaging the buerocracy etc., most 14 year olds do not do this and hence do not have a right to go to the polls. In addition to this imagine the campaigns that would result, its bad enough when politicians try to appeal to 20-somethings, imagine the teen target campaign attempts (Unnecessary futurama bit: Richard Nixons head singing "Remember what the doormouse said, feed your head!, im meeting you half-way you damn hippies" for his 3001 presidential campaign)