For confudes first-worlders: the lines to divide different generation are placed by the American culture. So you would divide generations based on things within that specific culture, such as historical events that affected that culture, technology advancement, and politics.
According to my date of birth, I would be considered a generation younger than what my familiarity with certain technologies would do. Because the rest of the world didn't change at the same time as the US, or the same way. So things like dvds, cds, iphones, etc, would become widespread later than it would in the US. Which means, two people born the same year but in two different parts of the world would be introduced to said technology (or political consequences, or fashion, or culture) while one was in elementary school and the other was in the equivalent of an high-school.