[Sims Mobile] How do I age up children to adults?

[MerryD31]

I’m not quite sure if you can help me but I figured I’d give it a try. I read your post & you seem to know how this game works much better thanI do. Using The Sims Mobile: I had a child who was EXTREMELY ready to age up but he turned into a full grown man. I’ve tapped on the family portrait & it said there are no open spaces. There is an open spot, (but I must add there is no plus (+) sign inside the box) where a roommate could go, but he will not go there. Do I have to go through the steps in Challenges for a roommate & will this change his status from son to Acquaintance or something else even though he’s technically my son? 
If you can help me that would we wonderful. If not, thanks for taking the time I presumed you used. I hope your question gets answers! 😁

[SalixCat]

@MerryD31 One option is to retire one of your playable Sims and then promote the son, but maybe you want to have all three Sims active at least for a while until they complete their stories.
How many playable Sim slots do you have? If you have two and want to add a thrird playable Sims, you will have to either buy the Sims slot with Sims cash or complete the roommate race quest to unlock a third Sims slot. The walkthrough is here: https://answers.ea.com/t5/Game-Information/Roommate-Race-walkthrough-unlock-your-3rd-Sim/m-p/7920676...