A common source of confusion when labeling generations is their age. Generational cohorts are defined (loosely) by birth year, not current age. The reason is simple, generations get older in groups. If you think of all Millennials as college students (18 - 22), then you are thinking of a stage in life and not a generation. Millennials are out of college and that life stage is now dominated by Gen Z.
Another example, a member of Generation X who turned 18 in 1998 would now be nearly 40. In that time, he or she cares about vastly different issues and is receptive to a new set of marketing messages. Regardless of your age, you will always belong to the generation you were born into. As of 2019, the breakdown by age looks like this: Baby Boomers: Baby boomers were born between 1944 and 1964. They're current between 55-75 years old (76 million in U.S.)
Gen X: Gen X was born between 1965 - 1979 and are currently between 40-54 years old (82 million people in U.S.)
Gen Y: Gen Y, or Millennials, were born between 1980 and 1994. They are currently between 25-39 years old.Gen Y.1 = 25-29 years old (31 million people in U.S.)
Gen Y.2 = 29-39 (42 million people in U.S.)
Gen Z: Gen Z is the newest generation to be named and were born between 1995 and 2015. They are currently between 4-24 years old (nearly 74 million in U.S.)
The term "Millennial" has become the popular way to reference both segments of Gen Y (more on Y.1 and Y.2 below). Realistically, the name Generation Z is a place-holder for the youngest people on the planet. It is likely to morph as they leave childhood and mature into their adolescent and adult identities.
The Baby Boomer Generation
Years Born: 1944 to 1964
Current Ages: 55 to 75
Generation Size: 76 Million
Generation X
Years Born: 1965 to 1979
Current Ages: 40 to 54
Other Nicknames: "Latchkey" generation, MTV generation
Generation Size: 82 Million
Millennials (Gen Y)
Years Born: 1980 to 1994
Current Ages: 25 to 39
Other Nicknames: Gen Y, Gen Me, Gen We, Echo Boomers
Generation Size: 95 Million
Gen Z
Years Born: 1995 to 2015
Currently Aged: 4 to 24
Other Nicknames: iGeneration, Post-millennials, Homeland Generation
Generation Size: Roughly 25% of the population