My 13 y/o, @ 6', 190# has facial hair, and won't leave the house if it shows, by his choice. If that changes, fine. My rules are that he shall do as he wishes with hair legnth, fuzzy goatees, etc, as long as he looks nice and well groomed in his chosen look. No purple hair, no mohawks, etc. He doesn't steal cars, smoke dope, or run wild.
That is what matters.
Bill