The Sim may be corrupted or broken for some reason. Is anything missing, like their aspiration or personality points? It's also possible that the cheat simply isn't working. I've never tried to use it. The regular in game cakes only work if they are one day from aging up or it is the day they are supposed to age up, is it within that window?
If nothing else is wrong that you can identify, if you are open to mods, I suggest you get the Simlogical Heirloom cake, which allows you to age Sims at any time (and kill elders). Try that and see what it does. I've been using it for years and wouldn't play without it.