According to a CBS news video, Echo Boomers (sometimes called Generation Y or Millennials) are the largest American generation since 1960. If you include Echo Boomers born from 1982 to 1995, there are roughly 80 million total. For reference and consistent date sake, Echo Boomer by my definition means a young person born between 1980 and 1995. This would mean that there's more than 80 million.
When I worked in the financial industry, approximately 25-30% of my calls were Echo Boomers. While this had been trending upward for the last two years, some of these Echo Boomers were excluded because they're too young (1993, 1994, 1995). As this generation matures, I expect that a third of financial customers will be Echo Boomers. From a business perspective, not only is this exciting news, but it also means that unaware companies, which fail to market well to Echo Boomers, will easily fall to companies, which have prepared for this massive demographic.
An example of this generation's size affecting business would be the housing market. A generation with over 80 million members may mean a generation that eventually will need more housing units (and depending on the Millennial marriage rate, the demand may be higher because fewer Echo Boomers will marry).
As a final note, notice that there is some disagreement as to when the Millennial generation begins. Even with the disagreement, however, the estimates are about 80 million (close to one-fourth of the U.S. population). An example for investors or traders, would be Generation Y's affect on oil prices, as more Echo Boomers, who drive, will cause the price of oil to rise in the long run (unless alternatives are developed within the car market that do not use oil).