Consider it one one of the latest indications that conventional notions of adulthood (i.e. getting married, buying a house and having children) are on the decline: Singles now make up more than half of the adult population for the first time since the government began tracking these stats more than 35 years ago. Heidi Moore, The Guardian’s U.S. finance and economics editor, says the financial benchmarks of adulthood have changed for millennials.