For whatever reason, age labeling seemed to become a more prevalent and emotional issue with the advent of the concept of Gen X, aka twentysomethings, slackers, baby busters and the 13th Gen ... as in the 13th generation since the founding of America.
—Cynthia McMullen, "Ageless, timeless?," Richmond Times Dispatch (Richmond, Virginia), April 29, 2004

"Generation X," for example, is now accepted almost universally to describe people born from the early '60s to around 1980 (the cutoff dates vary widely).

But that name, popularized by the title of a 1991 novel by Douglas Coupland, was rivaled for a while by such labels as "Baby Busters," a play on the baby boomers; the not exactly complimentary "Slackers"; and "13th Generation," based on the idea it is the 13th distinct age group since America was born.
—James Hebert, "Zoom goes the meaning of demographic term," Copley News Service, November 10, 2003

We label young Americans born between 1961 and 1981 the (Reactive) 13ers — partly because they are the 13th generation to know the U.S. flag, and also because of their lucklessness, the burden they feel from their "bad" reputation.
—William Strauss, Neil Howe, "The 'Constellation' of 1991," The Washington Post, February 24, 1991