If you let your 14-year-old plan to live in the house until indefinitely, they will plan to live in the house indefinitely. On the other hand, if you tell them to plan to move out, go to college, and be independent from the time they are 18 (less college expenses, which are the parent's responsibility), this will be their plan.
So which is the better plan? Which one to you want for your kid?
Keep in mind, that things do not always go according to plan. If my kids screw up at 20 and need to move back in, I will treat them with love and compassion, and help them as necessary. But that is not their plan.
Kids should have a life plan. I just don't understand the 'get them out when they're 18' thing though. Maybe it really is a cultural thing. My family at home has three generations living in the same big house. Grandmother is upstairs and son is downstairs with his family.
Another ENORMOUS contributor - parents today make enormous sacrifices to ensure their children do not have to face adversity, or difficulty.
Shielding children from adversity is always counterproductive, as real life is almost nothing but dealing with, adapting to, and overcoming complex problems.
Parents seem to have forgotten that character is largely formed by dealing with problems and difficulties, and it cannot be purchased or inherited.