Wow, I guess I didn't know that this sort of thing causes feelings to run so deep. I just figured- if people want to put studs in their cheekbones and stretch their earlobes and get a shag haircut or tatoo or alter their natural appearance in any way- shaving is something far less permanent!
At any rate- by the time I was 10-11, my mom and I were pretty much consensually living (more so as I got older- I never had a curfew, and pretty much informed her of things I was doing, and she did the same). One day I decided I wanted to shave, so I used my own money and bought some cheapo little razors and went to town. I think I nicked the backs of both knees, and that was what it took to learn to keep my legs/armpits/whatever at certain angles to shave them. I let my mom know what happened, and she bought me nicer razors.
For me- if my child wants to shave, she/he has my blessings. If not, the same thing. Who's to say they won't go through times where they will shave, and then not shave, and then shave again (and then again, there are similarities of style...)