I did not read this entire thread, just wanted to share how I age my rotating game. I play with all age related options off. No aging of anyone, played or not. Then on New Year's Eve (or whenever you feel a year is up) I turn aging on for everyone for just one night. Played, non played and NPCs - everyone will then add 1 year to their age. Then it is essential to turn those setting back off - I forgot once and played a week with full aging on before I noticed. Instead of going back to a back-up, I just continued with one extra rotations before the next growing up night.
I normally use the cake to age up sims, which feels a bit tedious when playing a full "universe". On a few occasions a sim aged up by "free will" before I get to it.