Meh-- I indulged this with DD starting when she was about 12-13 and had friends who wore make-up. Our major concern was that purchased items had to be safe for her to use (allergy concerns).
I taught her some technique, and let her experiment. Covered skin CARE more than anything else.
Now that she's 16, most of the luster is gone. She uses makeup to subtly alter her apparent age, which is socially/professionally useful as an accelerated person.
Nail polish was even earlier. Maybe 9 or 10?
I really don't wear much makeup now, and haven't since I was in my 20's, but I also think it's a useful skill and a personal decision.
