So what I wanted to do was adjust the lifespans of all my occult sims. I have EA aging enabled and made sure that the death: allow aging was set to true on SP at the town hall options. I've clicked on the Returner mod at city hall and then clicked General > By Tunable XML > Sims3.Gameplay.ActorSystems > AgingManager and adjusted the fairy multiplier, yet my active fairy sim's days stay in sync with the normal sims and continue to age up. Does anyone know how to fix this or why it's happening?

That setting could need a save as, exit the game completely out and reload the game. First try selection g a different household sim though and back, sometimes the UI needs a little reset like that.