Seeing my sim's age?

@toflubrains It's somewhat relative to the lifespan settings you have your game set to in Options Menu > Game Options > Gameplay in your game save:


You will see the age it in terms of number of days remaining in the life stage they are in (Baby, Toddler, Child, Teen, YoungAdult, Adult, Elder). Plus the number of days in each life stage varies by whether your settings are to long, normal or short lifespan.

There's a great article on aging and the Sims that may be helpful here, including a chart of how many days per lift stage per lifespan setting: https://www.carls-sims-4-guide.com/tutorials/sims.php