There are 2 auto aging options. Turn off the one for played Sims. (And unplayed sims, if you want). Progress that is already in the bar will be retained, but will not fill up further until you turn aging back on.

Do unplayed Sims age up?

Yes: The sims inside these lots will keep aging even if you are not playing them. 2- Playable Sims that live on the map but you never played them before (The plumbob icon for these lots on the map is just in grey color).

Do Sims age in Sims 4 when not playing?

The Sims you are not playing will not freeze in time like in TS2; the days pass for them, and they might not be at home when you go back to them, but they will not have had days subtracted from their lifespan (i.e., they don't age when you're not playing them).