Yes, 14 year olds should vote: for their class president, for homecoming king & queen, for representatives of the youth's interests in the neighborhood or the sporting associations and clubs. All this, as a way of getting to know the importance of it all.
Citizenship comes with obligations. Should a 14 year old felon be treated like a criminal? Should a 14 year old choose between school and work? Should a 14 year old join the army?
In Mexico, minors "vote" during general elections, but not electing representatives, but answering all sorts of questions in a consultation process. Specially the younger ones are eager to do something similar to the grown-up thing.
This were the results in 2003:
Children and Youth Survey 2003 (in English)
The idea is not new. There's a 1968 film in which a US Presidential candidate has the motto "Fourteen or Fight!". Actually, it's quite a dumb anti-youth film, IMHO.
Wild In The Streets