I don't know if you're opposed to using mods, but TwistedMexi has mods that allows you to set the age of Sims without leaving your household or having to place new ones down, etc..
This one has the set age cheat as part of it, but over all the mod unlocks a wide range of cheats that were taken away from us awhile ago: https://www.patreon.com/posts/cheat-fix-for-22697405
This one is just for setting the age, though it was last updated in Nov. 2018:
https://www.patreon.com/posts/cheat-fix-for-22697405
In either case, you'd open up the cheat menu and type in "tm.setage " and they should age up accordingly.
