I keep detailed track on each sim's properties and other values, so I never just give the youngsters some money unless they could get it as heritage in-advance. Most of my households have just their main home. After university my sims will normally move into a smaller home on their own. When parents gets very old, they might swap homes, or the main heir will just move back home. I need this kind of realism in my game, because it also provides some challenge. And it makes sure that sims who don't care to get a decent job, will normally be stuck with their small rented home for decades :)
