According to Morningstar economist Bob Johnson,
population growth recently has only growing about 0.7% - 0.8%, while historically it has been as high as 1.5%.
Probably why you hear 100,000 - 125,000 jobs need to be created each month in BLS report to keep up with new entrants into work force. The 250,000 number I think is for the ADP report, and again we don't know what underlying population growth that assumes.
2.3% real GDP growth might in some way be equivalent to 3% real GDP rate of growth now vs. historical norm, also because of decreased population growth.
Regarding seniors, they are staying in labor force later than they have done previously, taking away jobs that would normally go to the youth (
http://www.csmonitor.com/USA/Society/2012/0902/The-silver-collar-economy). Some may have never saved enough in investments to retire, and others just got walloped like everyone else when stock market crashed in 2008.