@TariaC Potion of Rejuvenation likely doesn't keep their current age forever, it's only an Adept potion and would negate the usefulness of the Master level Potion of Immortality.
I'm willing to bet it does the same thing as the Potion of Youth and Age-Away Serum from GTW, it probably only resets them back to day 1 of their current age group. They'll need to keep taking it before aging up to stay in that age group.
Unfortunately i've never seen anything that rolls you back to a previous age-group or stay in an existing age group... without mods that is... or being a vampire.
I tested it in my own game and thought it had worked. Also by the way it's description was written "A potion to allow a Sim to remain at their current age." I thought it meant they would stay that way. But you are right it just resets it.
I'm sorry for the misconception.
It's nice to had a choice what age you want to use potion of Immortality in age sage, rather than limited choice by elder sage, maybe even child stay child if drinking potion of Immortality.
