they should start at the least 10 or when they come to you to talk about when its getting hairy and their getting teased but i recommend hair removal cream
when you get underarm hair just do NOT shave pubic hairok That isn't a bad answer theres some good advice in it! Anyways I'll add to it-Around ages 11-13 make sure you have your parents permission...
At whatever age that you begin developing facial hair, which is generaly whenever puberty starts. Basically, when you start growing hair on your face, you start shaving it. It doesn't make much sense...