This helped on PS4. I'm trophy hunting so, I don't use cheats. What I did to fix it is really annoying because it does take away your relationship with the kitten. Since you cant Age up a sim or pet in CAS without cheats. The only option is to save the Pet to your gallery then, remove the pet from your household. Add it back and it will allow you to edit the Pet as if it had never been in the household. Hope this helps for anyone on Console who may be experiencing the same thing and don't mind sacrificing relationships.
Product: The Sims 4
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 22.214.171.1240
What expansions, game packs, and stuff packs do you have installed? Cats and Dogs, and Holiday Celebration pack.
Steps: How can we find the bug ourselves? Try to age-up a kitten with an age-up treat.
What happens when the bug occurs? The kitten can eat as many as she wants while on the home lot and nothing happens. It's like giving her a normal treat.
What do you expect to see? I expect to see my cat age up.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure
I've fed my kitten seven age-up treats to no avail. I've waited overnight (in-game) and still, nothing has changed. She is still a kitten.Yes, they were on the home lot.
Edit By Crinrict: Added Tag to Title
Same. Adopted two strays. They had kittens before my Sim had her baby. That Sim is dead now and her baby is now a Young adult and the two adult cats are still adults. All the kittens are still kittens. Age up treats do nothing. I don't have mods.
I've tried aging up multiple kittens on both pc and playstation with the age up treat and after I give it to them nothing happens
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I had two adult cats from the same litter, one of them aged up to elder but the other one didn’t. I gave it a few days to see what would happen. I did not try the aging treat. After a few days, he did age up. I thought it was interesting that both times they aged up, it was right after I had just loaded their property. I would suggest that anyone having cat aging issues try exiting the lot and reloading it, perhaps even the entire game to see if it gets triggered.
When I give my kitten an age-up treat, the kitten will not age up. Adult cats will not age up either. However, cats have no problem aging down, and dogs have no problems at all. I used the Playable Pets mod to check the kitten's queue as he was given the age-up treat and the interaction appeared, but immediately got cancelled. Waiting for the kitten to age up naturally did not work as the kitten never aged up. I suspect the problem may have to do with a faulty or missing animation for cats aging up.
My (adopted) kitten has been a kitten for about 40 days, which is fine personally because my Sim is a vampire.