Board Thread:Questions and Answers/@comment-29325824-20180306210930/@comment-29435884-20180307121238

The Demon Lord herself is just a crazy powerful succubus, she's 1000 and something and still going strong. Druella's profile mentions she has a lifespan 'that can even be said to be infinite.'  Going from that, I'm guessing the most powerful living mamono can obtain immortality (or something similar) through sheer magical ability.