Anyone who lives in the state of California can legally purchase and wear a bullet proof vest in California as long as the person has not committed a felony or is a felon.
As long as you have no felony convictions you can purchase a bullet proof vest or other body armor online or in stores that sell the bullet proof vests.
With what's going on today with all the shootings and stabbings at concerts etc it's a good idea to wear a bullet proof vest just in case of a shooting.
However in schools students are not allowed to wear bullet proof vests which makes no sense because the bullet proof vest could save a students life in the event of a shooting again.
Still a bullet proof vest doesn't protect you fully because you could be shot in the head which is deadly as well but a bullet proof vest can protect you.