Over the past 100 years or so, as the industrial revolution and increasing longevity have given young people more time to mature and allowed older people to live into their 70s, 80s, and 90s, new terms have been created:

o “Gerontology” was invented by Russian biologist Elie Metchnikoff in 1902

o “Adolescence” was coined in 1904

o “Teenager” in the 1920s

o “Empty nest” in the 1960s

o Distinction between the “young old” and “old old” is from the 1990s