Seniors above 65 aren't considered part of the workforce. But many are. In the US there are 1.2 million people over 75 still at work, a number that has been growing, corresponding to 0.8% of the total workforce. About 90,000 people enter the workforce each month from school and legal immigration. If another 25,000 seniors per month decide to keep working, then the economy has to generate 115,000 jobs monthly to avoid a rise in unemployment rates. This week "Zero jobs" has been in the news but the truth is more like 100,000 more people are unemployed at the end of August than were at the beginning.
Source: John Mauldin's "Frontline Thoughts" (free subscription).
Related: Chart shows how many jobs needed to drop US unemployment rate