My sim aged up on Tuesday. Nothing in calendar for that week's Sunday, and nothing happened on that Sunday. However, when Monday arrived, the graduation ceremony did appear in the calendar, and the game did the pop-up on Sunday, and my sim could go to the graduation just fine... almost two weeks after aging up. I mean... she had twins at that point, and was level 7 in her career, but off to the high school graduation!
Proms never appeared in her calendar, but worked just fine. Graduation did appear on calendar and ..sort of worked. My problem, which is not related to the calendar bug or event-occurring-bug is that there was no principal in the event (she had died in neighborhood stories and the game hadn't created a new one, since no sim had visited high school after that), so there was no ceremony of giving diplomas, throwing hats, or getting graduation picture. I made a separate bug thread about that, just wanted to pipe in the calendar bug that it -can- last an eternity before it's scheduled in.
These things took place with aging on with normal lifespan. I have had a perfectly 100% successful graduation ceremony in my aging-off save.