That just shows how many people own a house?
It could be that youngsters then left school, jot a job, saved some money, bought a house, and now youngsters prefer to piss it up in university rack up debt, go on a jolly around the World for 3 years, come back and go time to settle now lets by a house, oh dear I can't i've got no savings an average job, shed loads of debt, and it's all the torries fault.