@PLURSimmer to make birthday cakes you just click on any cake you've made and add birthday candles. Then any Sim can be aged up by blowing out the candles. It shouldn't need cheats to age up any Sim. The infant will need an adult sim to give them help with the candles while held, but it has always worked for me.
Or you can turn on ageing for them to age up but I prefer not to do that as I play with ageing off. I think it's 5 days to age to toddler. It would be a bit rough if their parent aged to elder as they aged to toddler or child! (Full disclosure, I accidentally did that once! Quick, exit without saving 🧑🦳!)
I know that some players use cas.fulleditmode to age up Sims but I've seen reports that it hasn't been working properly recently so I don't know if that's worth a try. But it shouldn't be necessary because the candles should work. You don't need a high skill and you can use any cake at all. I usually go for chocolate! 🎂
