I've never seen that before, but they have defined Generation X as people who were born before 1980. On the other hand, people born after 1980 are called Millenials.
So, is 1980 a year where everything changes? Well, yes and no. A recent study has shown that Millenials are slightly more addicted to technology, or their lives revolve around it more than GenX, so they are probably more bound to carry MP3 players, USB sticks, fancy cell-phones, etc. Also, Millenials are more likely to spend a lot of time on social networking websites, like Facebook and MySpace. Putting that in mind, Millenials are more likely to use their computers for both business and personal matters, Millenials are more likely to visit suspicious websites, Millenials are more likely to install pirated software, and last but not least, Millenials are more likely to introduce their MP3 players, USB sticks, and their cell-phones to your business network.
Therefore, Millenials impose a bigger security threat than GenX.