Re: Alexander aged up, when I wasn't playing him, with non-played aging turned off.
You just need to change the setting to only active household aging (see pictures)
Basically what you did when you switched to him, then you made the household played and played Sims age in your game so after a while, he aged up
OR
after changing to a family make sure you mark them as unplayed again in the household manager by clicking on the plumbob picture (see second pic)
