How can I not age a Sim?

sorry but there is no way. you either stop aging for the whole family or not.

The Generations expansion pack for Sims 3 introduced the "Young Again" potion (returns the drinker to day one of the Young Adult stage) and the 65000-point Lifetime Reward "Age Freeze Potion", which effectively locks the drinker at the age they currently are (Sim won't age unless they have a birthday party to force it). The Age Freeze potion is the only thing that truly locks your age while everyone around you continues to age.

Beyond that, each time your sim eats ambrosia they move backward one day until they reach day 1 of their current life stage, but ambrosia can be difficult to make until you have your sims pretty well established in their skills.

These are all in-game mechanics. There are, of course, mods to allow you to adjust lifecycle of sims. You can even change their life state from within the Create-a-Sim interface if you've previously done the "testingcheatsenabled true" cheat.

If you're looking for mods to do this, you may want to look up the Awesomemod or twallan's MasterController.

Hello:)

Well ok, go to the family that you do not want to age, click on the options button (The three dots on the bottom left corner) now go to game options via a tab that appears when hitting options, near the bottom of the tab there is something that says enable ageing, there is a tick mark beside it uncheck it and save your changes. Hey presto Sims will not age in that family:)

B

ps.

I found this video on youtube on how to do it If you can't follow my Instructions.

http://www.youtube.com/watch?v=nMIP4G5uOzw

edit*

I am sorry I did not notice that you said only one sim. The only way of doing that is to move the sim elsewhere then turn off the ageing or else you will freeze the ageing on all sims on the current lot.

well i dont know what its like in sims 3 but in sims 2 there is a potion you can buy with aspiration points... look on the cheat codes websites it might say it there :))

hmm this is a toughy i'm not sure this will work but try it, Turn off aging then use birthday cakes to age the rest

here is what u do :

just keep eating life fruits , each life fruit gives u an extra day to live and yes u can eat 100 life fruits and get a 100 extra days to live ( easy :) )

http://www.youtube.com/watch?v=LYDMRS7VuL4

I was about to say something, but catherine beat me to it