Particle, that criteria has three flaws. First, it is a trivial matter for a 13 year old to claim to be 14 in order to swear like a sailor. Second, it is a trivial matter for a 14 year old to claim to be 13 in order to annoy half the people on the server by being a catalyst for censorship. Third, keeping track of who is 13 would quickly become a daunting task.
I say censorship should instead be based on the time of day; for example, during the day, all swear words are censored, but during the night, only level three words (racial slurs) are censored.