Neuroscientists at the University of Cambridge analysed thousands of MRI scans and found that the brain passes through five structural phases. They are childhood (birth-9), adolescence (9-32), adulthood (32-66), early ageing (66-83) and late ageing (83+). These phases are marked by key turning points at ages nine, 32, 66 and 83. Researchers said the brain hits "adulthood" at 32.