About improvement on age and question online

@AnmDragon298 , if you only want some Sims in your home to age but others not to age, you can do a work around were you can use your Satisfaction/Aspiration Rewards points at the Rewards store on your Aspiration Panel to purchase the Potion of Youth.  This will set your Sim who drinks it back to the beginning of their current life-stage. 🙌 So if you are a teen , for example, you cannot become a child or toddler again, but you can reset the clock on your teen life-stage.  It is best to use this near the end of a life-stage since it is a bit of a waste to use it at the beginning. 😉  (I have never tried it on a toddler, so I don't know if they can use it, but any other Sim from a child to elder can use it!   I know this isn't the same as what you had in mind, but it is a nice work around and can be very helpful if you are a story teller, or just really like a certain Sim at their current age! 🥰

As for allowing Sims in the world to marry and have babies, that kind of happens in certain situations.  Ever since one of the updates this year, some Sims will call your Sims from time to time asking advice, such as if they should have a baby or not.  If you say yes, then that Sim will become pregnant (even if they are male! 🤨😲😅) and later have a baby. I don't recall if they ask to get married or not, though. If you tell them not to have a baby, then nothing will change, so the choice is still yours.  But it is nice to have this opportunity from time to time! 😎