Oh, definitely something any sane GM would veto, just going over the mechanics of it.
Hmmm, I agree about it fitting best for Blood Magic. Perhaps an Advanced Metamagic (call it "Life Stealing" or something) that has Sacrifice or Canibalism as a prereq. De-ages 1 year per Essence, perhaps.
If nothing else, it's a great excuse to have a first-generation goblinized Ork Blood Adept (Twisted, too, of course) still walking around in prime fighting condition.