Can you find statistics on employment for those over 55? If their employment participation is not dropping then they are not retiring and the losses have to be coming from lost jobs, not retirements.
I found stats and numbers for 65 and older on
Table A-6.
The numbers are divided into Disabled and not Disabled. From April 2011 to April 2012 a total of 1,423,000 65 and older left the labor force. That's an average of 118,580 per month. The numbers are not seasonally adjusted.
IIRC normal population growth is about 125,000 per month and approximately 125,000 new workers consisting of green cards and temp work visas come into the US each month.
Here's an
article with some interesting tidbits regarding employment and unemployment.