ACR counts a Sim's age in days to calculate the pregnancy chance, at least. There's some info here:
https://modthesims.info/t/568322

Another question: How do I trick the game into thinking an already-made adult Sim attended college? If I give someone a degree with batbox and then subtract the days manually, it just fills up the lifespan bar.

EDIT: In SimPE, if you go to a Sim and use Extended Browser, there is an Age Duration. I think that will work.

@Bulbizarre In case of ACR, please first check how my mod works with it without adjustments. It looks like checking how my mod could potentially affect ACR would require diving into its code and trying to understand how it technically works.
Regarding the second question, I'm glad you figured it out yourself

@Bulbizarre are you talking about whether or not ACR's fertility curve needs to be adjusted? If so, I would think not, as long as you are making sure that sims who skip Uni get the same amount of days as those who do go to Uni. You could probably test and see if your YAs have the same fertility chance as sims who did not graduate.

This mod is perfect! I always wished my sims who didn't go to college weren't suddenly older than their friends when they got out of school. And I love that I can use it with the Slow Aging Controller.