To cope with what demographers call “super aging societies,” policymakers in East Asia initially focused on trying to spur births and tinkering with immigration laws to shore up work forces. Such measures have done little to alter the aging trend line, as fertility rates have plunged and many countries have resisted large-scale immigration plans. That has left employers desperate for workers. In Japan, for example, surveys show that as many as half of companies report shortages of full-time workers. Older workers have stepped in to fill the gaps. “We have…