Returning to the OP, when the 60/65 retirement age was set, people worked from 15 to 65, 45-50 years. Half the kids go on to higher education of some sort, so they don't start until 21 or 22, and so from a contribution basis alone they'll have to work those extra years. It used to be the deductions were roughly proportionate to a life expectancy of 70, 5 years after 50 at work, 10% deductions for pensions and more for health, but the NHS has pushed that to nearer 80, and so 15 years after 45 at work (this is Osborn's 1/3) means deductions should have shot up. They haven't and so it became unaffordable. Work longer and things come back closer into balance.