Life expectancies have risen dramatically over the last 50 or so years, incomes have risen, length of time spent in education has risen, marriage rates dropped off and later in life, birth rates dropped off substantially and nowadays 30+ years old is the average first birth age.
50 years ago people used to dig holes with shovels, now machines do it all.
50 years ago, parents couldn't afford to support their kids into their late 20's
50 years ago young people couldnt support themselves in their later life unless they learn the tools of their trade, i.e. working, now formal education has taken over from learning on the job.
I think the reason is mainly the fact that marriage and child bearing occurs later in life, i.e. no strong need to leave home.
