You can have them drink the potion of rejuvenation to reset their current age meter, even though there is already a buyable potion as a reward trait with the same effect. You could even wish the same effect if you like to gamble. Or even drink the life of essence for the same effect from the cow, if you like killing off other sims. It's like there is this constant theme of reselling concepts that are already in the game but just in a different way. It is important that if your sim is capable of aging as a young adult, assuming you would like to keep them there, that you figure out how you are going to do that beforehand. Apparently wishing for life right now does not reset their age from elder to adult or adult to young adult. So that means if they hit the next level, you'll have to cheat them back to the previous age group, unless there is something I don't know about. So I say that to say this... if you prefer an npc (some of them are already immortal) or unplayed sim to remain at a certain age, you need to either make them into a vampire, turn off aging as a whole in settings, continue to frequent the houses of unplayed sims to drink an age reset potion, or make into a spellcaster who will stop aging at elder. As an elder they can still die of overexertion and laughter, so I just assumed this was the reason they were still dying even though they are immortal. They just released a new update, I'll do a bit more testing to see what is happening here. I'm not sure if this is designed as intended or just the result of lazy coding. I will say though, that so far my mermaid who has drunk the immortality potion has been the only life state that did not die during this process. I'm not sure if there is anything special about her besides the fact that she is a mermaid. You can make the revival process easier if the spellcaster is living with a vampire, so that you still can access the house and use a necro+dedeathify combo to rewrite the problems. They still need to be readded to the household, but at least they added a new interaction on the computer to make the process more streamlined. Sorry for my rambling.
