Hahaha! I'm the only person who said "under 14", awesome!
But yeah I think when I was 13 I was more knowledgable about the political process than at least a quarter of the people over 18 at the time.
There should only be three requirements to vote.
You MUST be a citizen.
You MUST be older than the legal working age (usually around 13 or 14, but this can be as low as the country wants it to be).
You MUST have registered to vote. Registration would entail, among other things, a political awareness test, in which you must prove that you have at least a basic understanding of the political process. (Works similar to a driving test)
For people over 25 registration is mandatory, and thus voting is completely optional until you turn 25. People over 25 who cannot complete the test will be fined, in the same manner as if they incorrectly filled out their voting pamphlet.
Giving teenagers the right to vote means the education system won't be left to the mercy of concerned parents.