Be a U.S. citizen. Be a resident of the Arizona county listed on your registration. Be at least 18 years old on or before the date of the next general election. NOT be convicted of a felony (or have had your civil rights restored). NOT be declared "incompetent" by a court.
at least 18 YEARS OF AGE by the next general election
NOT a convicted FELON, unless civil rights are restored
NOT adjudicated INCOMPETENT (A.R.S. § 14-5101)
Explanation:
Those requirements are set by law in Arizona and they can all be found in the Arizona Law. Many websites, like the Service Arizona have detailed information on how it the rules work in order to register to vote.