100 Baby questions

Pregnant sims can't age up to the next life stage, but they still age within their current life stage

I believe that Sims 4 sims don't age during pregnancy, so that may be where the information came from. As wendyyi1 said, pregnant Sims 3 sims will progress within their current life stage but not age up into the next one until after birth.

As for lifetime rewards, I personally would feel that the Age Freeze potion would be too cheaty, and probably Young Again as well. But if your matriarch wanted to eat life fruit, or eat ambrosia, or drink life fruit nectar, that seems more fair, since all of these options take at least some work and aren't permanent. But it's your game, you should play the way you want.