What age is appropriate to dye your child's hair?

My daughter is almost 9. She has been asking me for a few years now to dye her hair. I still feel like she's too young. I wasn't allowed to dye my hair till I was 12, so now I have that stuck in my head as a magic number. Should I let her dye it now? I don't want to be an over controlling mom, but I don't want to seem like a bad mom for letting her do it. I dye my hair every 6-8 weeks, so she's seen me dye my hair a lot. I'd if she wants to do it because she sees me doing it or if she really wants to have her hair a different color. I let her cut her hair however she wants, except recently she wanted her hair long on one side and buzzed on the other, and I had to draw the line. So we agreed on a pixie cut instead. Help!