Our economy is beset by chronic unemployment. People under 25 have a hard time finding jobs, while for those over 55 it's extremely hard to find a new job if they lose their old one.
One way to help both the over-55's and the under-25's is to make it easier for the older workers to leave the job market. If they could begin collecting Social Security and Medicare at full-benefit levels, more jobs would open up due to earlier retirements - and those over-55's who are unable to find jobs would be better able to survive after unemployment benefits run out (with at least that minimal income and lower medical costs).
This is better than reducing the payroll tax - it would stimulate the economy with money that would be spent immediately, and would open up jobs for younger workers.