I have decided to go ahead and turn on aging. I have not yet played that way. However... My main Sim I want to NOT age up. Without cheats, what are my options? I know I can use the potion of youth. ...
Ambrosia, but seeing as that requires a Potion of Youth.... You can wish for youthful energy from the wishing well, obviously not anywhere near 100% chance though. You could use the essence of life from the cow plant. http://www.carls-sims-4-guide.com/help/immortal.php