Presidential Age Limit

On the heels of the Iowa caucus, let's ask about the requirements to be President of the United States.  It is written into the second article of the Constitution that to be eligible for the position, one must be thirty five years old.  Is this something we think ought to be maintained or is it groundless, anti-democratic age discrimination?  If you are old enough to vote, shouldn't you be old enough to run?  I'm not saying that there is a given twenty two year old I would vote for, but why limit that person's right to seek the office?  Plato argued that we shouldn't even educate people until they reach forty, so offering such folks the most powerful position in the world may not be the best idea.  Then again, the electorate would be able to decree with their ballots that the person was too green and not yet ready.  Why shouldn't we have the option?  Is the presidential age limit legitimate or illegitimate discrimination?