I can't help you on the in-game options for aging up an Infant with aging off -- I haven't looked for those yet and would have assumed that I could bring them to a cake, like a Toddler -- but you have two ways to do it without aging up other households. One is to turn aging on for ONLY the active household (this is one of the ways of setting it up in Gameplay Options). If you use mods, you can use UI Cheats Extension to change the number of days within the age range that your Sims is and skip most of that added time ("Right click on the age progress bar to add/subtract the number of days that have passed at the current age stage").
The other is to age them up in CAS, however there's currently a bug with cas.fulleditmode connected to having extra traits, and selecting Toddler traits is likely to trigger it. It's a really awful bug that even spreads to other saves, so I wouldn't touch that method till it's patched.
