You target a creature you can see within range, putting its physical form through the devastation of rapid aging. The target must make a Constitution saving throw, taking 10*D12 necrotic damage on a failed save, or half as much damage on a successful one. If the save fails, the target also ages to the point where it has only 30 days left before it dies of old age. In this age state, the target has disadvantage on attack rolls, ability checks, and saving throws, and its walking speed is halved. Only the wish spell or the greater restoration cast with a 9th level spell slot can end these effects and restore the target to his previous age.
This is a Dunamancy spell and it should be discussed beforehand with your DM.