Delores's Life Siphon

You steal the youth from a creature and add it to your own. In order for this spell to be successful, the creature must be within 10 feet of you for the entire casting time of the spell. If the creature moves further than 10 feet from you at any time during the casting of the spell, the spell fails. 

On a success, 1d8 years of the creature's life are stolen and your physical age is reduced by the same number of years. Your natural lifespan is also extended by the same number of years. You can continue to cast this spell on the creature until they are magically aged to 80% of their natural lifespan, after which their body is too frail to survive the casting of the spell and they die.