I’ve blogged before about the cultural differences between older and younger Americans in the workforce. Some observers consider the differences to be of historic significance compared to previous eras, due to the confluence of various “macro” forces driving change at an extraordinary pace.

And somewhere along the way when few were looking, the millennial generation has now become the largest cohort in the American workforce.

And it isn’t even a close call: As of this year, millennials make up nearly 45% of all American workers, whereas baby boomer generation now comprises just over a quarter of the workforce.

According to a new report by management training and consulting firm RainmakerThinking titled The Great Generational Shift, there are actually seven groups of people currently in the workplace at this moment in time:

• Pre-Baby Boomers (born before 1946): ~1% of the American workforce
• Baby Boomers first wave (born 1946-1954): ~11%
• Baby Boomers second wave (born 1955-1964): ~16%
• GenXers (born 1965-1977): ~27%
• Millennials first wave (born 1978-1989): ~27%
• Millennials second wave (born 1990-2000): ~17%
• Post-Millennials (born after 2000): ~1%

Personally, I don’t know anyone born before 1946 who is still in the workforce, but there are undoubtedly a few of them — one out of every 100, to be precise.

But the older members of the Baby Boomer generation are fast cycling out of the workforce as well, with more than 10,000 of them turning 70 years old every day.

By the year 2020, the “first wave” Boomers are expected to be only around 6% of the workforce.  Meanwhile, Millennials are on track to represent more than 50% of the workforce by 2020.

Now, that makes some of us feel old!

The Great Generational Shift report can be downloaded here.