A problem of ages

[Whitewings]

I want to create a family consisting of a young adult Sim and her toddler sister, but despite my best efforts, can find no way to do so. And yes, I have tried creating a full family, then aging her using cheats and cakes. It doesn't work; she won't age past a teenager.

[Pam]

You have to wait a few Sim days before aging with birthday cake again.  If you're trying to do it immediately after the first one, it just may be too soon.

[IloveLlamas]

Like Pam said, you have to wait for cakes. Or wait for their time meter to fill up.

[Saltypaws]

Although, with the testingcheats on, you can age up from baby to adult, one right after the other.  I have only done this a couple of times, but it does work.  I am not sure what I was doing at the time that I wanted to age the sim up, I think that I was actually testing it to see if it did work, because someone had said that they had tried it and it didn't work for them.

[athena]

I've done this before. No need to wait for the time meter to fill up. But after the cake, you have to wait perhaps around three days before you can age up using the cake again...You have to be ready because most times a negative moodlet called "Aged up too soon" will appear after the aging up process. Good luck!

[Pam]

Salty's right.  You can enable testing cheats, then shift-click the Sim you want to age up.  Select Trigger Age Trasition.