Give me your input please!

At what age do you think it's okay to have your daughter start shaving her legs??  My daughter is mature for her age, and I do have her shave her underarms already.  She has been begging me to let her shave her legs (she has taken the razor to her legs a couple times thinking I wouldn't notice) but I don't even know what a good age is to start shaving.  Thank you for any input you have.