I think it has to do with "life stages". I mean, when you graduate highschool and go to university, your life is different than it was when you were in high school. It is just one year, but it is one full of changes. What you want at that point is different than what you wanted then.

The next one is usually when you finish university and get your first "serious" work. Then you want to become independent and not share a house with flatmates. You might consider sharing with a partner, but not with flatmates.

And that continue. So most of the time, the 20 something, is at a different life-stage than the 30-something. Different wants, different needs, different lifes. It could work, but it is more difficult.

So while for a short term thing might not matter, for a long term relationship is way more complicated that there is complicity and mutual understanding.