Makeup - do you don't you?

My 8 year old has decided she would like to wear mascara for her dance festival tomorrow?  The question is do I let her or not.  It's not something I have ever allowed her to do as I don't think they should grow old before their time and they should be able to be a child for as long as possible.  What do others do?  Do they think I should say yes or am I starting her on a road to being old before her time.