Im 14 and a freshman in highschool for this years ski season When you race should start using shin guards?

You only need shin guards for racing in slalom, and they are only effective if you are good enough to hit the inside gate with your shins or boot tops. To do this you will also need to learn how to cross block the gate with your outside hand and you will need handguards on your poles: a helmet with chinguard is also a good idea if you start racing slalom. No ski racing gear is cheap, so unless you already know how to race slalom, I would wait and see if you will get to do this event and have the quickness required.