A substantial portion of older Americans now in the work force chose to return there after retiring, and how well they're enjoying their labor now depends a lot on whether they're self-employed, according to two new reports.Posted by James Zellmer at December 22, 2005 8:24 PM | Subscribe to this site via RSS:About 10% of workers 40 and older are retirees who've returned to the work force, according to a recent survey that screened more than 17,200 workers to find retirees who went back to work, conducted for Putnam Investments by Brightwork Partners, a research firm.