Which age group saw the largest increase in employment during the past 20 years?

I'd speculate (although it's not really speculation, just common sense) that the age group that has, percentage-wise seen the largest increase in the past 20 years are those born ~1980-2000, so ~21-40.

The oldest of those folks were just getting into the workforce 20 years ago. Those in younger age groups aren't (at least not in large numbers percentage-wise) in the workforce yet, and the older age group had already been in the workforce. QED.

I guess the long-feared generational war is finally upon us.

100% of the 11.8 million jobs created in the United States since Dec 2000 have gone to Baby Boomers.