My daughter is 12 and in 7th grade this year. She has light blonde hair, so that may make a difference, I don't know.
She doesn't wax. She doesn't even shave her legs. And just barely started wearing any kind of makeup--and even that she skips sometimes... it's just a powder foundation, a little natural looking eyeshadow, mascara sometimes, and lip gloss (not lipstick not lipliner).
She looks VERY natural. Not made up at all.
As far as when is it appropriate? Depends on the kid.
I am 45 this week, and I have NEVER waxed my eyebrows. Never needed to. I expect my daughter won't need to, either. No unibrows, here, and what we do have is light and doesn't stand out.
I just recently heard, however, (from a good friend of mine, not a student/kid) that this age group is now starting to shave their private areas already. And that it may be common to do so, and do so completely.
It was news to me, and nothing my daughter has asked me about.
Maybe take a look at your daughter's friends and SEE what they are doing. DO they wax? I would think you would be able to tell, or ask their parents.