A doctor or pediatrician can prescribe anyone of any age marijuana in the state of Arizona. However, typically a caregiver is assigned to a patient in order to administrate, grow, and dispense the marijuana to the patient. Caregivers must be 21 years of age. Otherwise without a medical card, marijuana possession in Arizona is a felony.
You have to be 18 to get a medical marijuana card in Arizona, or have your legal guardian registered as your medical caregiver. Then you are all good to smoke and eat and use as much marijuana as you need to alleviate your symptoms, within certain maximum amounts that can be legally held at any given time.