Immortality Potion Doesn't Work When Changing Household

Do you ever actually read the trait description?

Immortality prevents death from old age, what part of that implies you gain eternal youth? your sim will still age into an elder as intended, you need to consume potions of rejuvenation every now and again to stay young and it gets better, you need to direct the sims to consume those potions because they will not do it by themselves and if your not currently playing them they may age up on you.