If you don’t want your Sims to get old and die, you can turn off aging in the game settings. You can also slow down the aging process or use a mod to stop aging for specific Sims.
To stop Sims from aging, go to:
Game Options → Gameplay → Auto Age
Turn off Auto Age to stop the aging process.
You can also change the Sim Lifespan setting if you don’t want to disable aging completely. Set it to Long if you’d rather give your Sims more time in each life stage.
If you only want to stop Sims that you’re not currently playing from aging, you can change the separate aging setting.
Go to:
Game Options → Gameplay → Auto Age (Unplayed Sims)
Turn off this option to prevent unplayed Sims from aging while you’re playing other households.
This is useful if you want your played household to continue aging normally while keeping other Sims at their current ages.
How to Stop One Sim From Aging
The base game doesn’t have an option to disable aging for just one Sim.
If you use MC Command Center, you can flag individual Sims for No Aging or Immortality.
This gives you more control if you want most of your Sims to age normally but want to keep one particular Sim young.
Turning off aging doesn’t prevent you from manually aging up your Sims.
The easiest way is to bake a birthday cake. Once the cake is ready, click it and select Add Birthday Candles. Then have the Sim blow out the candles to trigger their birthday.
If you don’t want the Sim to age up, don’t let them blow out the candles.
Some occult Sims have ways to avoid the normal aging process.
Vampires don’t age like regular Sims, while werewolves can also unlock abilities that affect their aging and lifespan.
So if you’re looking for an immortal Sim without constantly changing the aging settings, playing with an occult Sim is another option.