I think I agree with grumpyoldfella...I think that's a little young!  I have a 13 year old and she has actually (thank God) shown no interest in make-up.  However that's probably because she is going thru the adololescent acne phase.  Like mommy3, I would have no problem with lipgloss but that's where it would have to end.  My concern is make-up actually doing more harm than good on such young skin.  

I think we have to pick our battles though with teenagers...there has to be compromises.  Although my 13 year old doesn't wear make-up she does have purple hair...it's a very dark purple so it's nothing too wacky but we decided there's going to be things far worse than coloured hair that she may eventually want and at that point we may not be able to give in.

If your only worried about chemicals then you should check out natural make up. Even the mineral makeup, since most of it is all natural. If its just the make up because you dont want your little girl to grow up, then I would say give in a little. Not full face with foundation and all that, but a little rouge or eye shadow and lipstick, should make her happy for now. As long as your wife teaches her how to make it look good and not to over done.

My daughter is 12 (almost 13) and she doesn't wear make-up. Like yummymommy we compromise, dad thought she was a little young to put that "junk"(as he calls it) on her face, but we decided to let her get a second hole in her ear on her b'day (which is soon). She was happy with that and had no complaints. We try to let her do more things as she gets older and more responsible but at the same time keep her loking and acting her age.

Mother to 5~

My dtr. is 12 and wears a little eye shadow and blush. Most of the girs in her class do as well. I won't let my dtr. highlight her hair though b/c of the damage those chemicals can do to hair.