Aru Majo ga Shinu Made

Magic is all Meg Raspberry has ever known. Being raised by Faust, the Eternal Witch, Meg wishes to become a witch as great as her master. However, her life crumbles on her 17th birthday when Faust delivers the worst news possible: Meg has one year left to live. Due to a congenital curse, after turning 18, she will age a thousand times faster than normal and then die in mere days.