—H. R. M.
Over the past decade, I have experienced many major life changes and transitions. One of the constants has been my ongoing collaboration with Harry “Rick” Moody, for which I continue to be so grateful. To all of the students and colleagues across the country who engage with our book, thank you for your generous ongoing feedback and support—I hope you see many of your very excellent suggestions manifested in this new edition! And, as always and forever, thank you to my family and closest friends for their encouragement and support. Where would I be without your love?
—J. R. S.
SAGE and the authors gratefully acknowledge the contributions of the following reviewers:
Monika Ardelt, University of Florida
Lisa Borrero, University of Indianapolis
Jessica Clontz, Pennsylvania State University
Han-Jung Ko, Central Michigan University
Esther Kreider-Verhalle, York College, City University of New York
Kate de Medeiros, Miami University
Veronika Ospina-Kammerer, St. Leo University
Ebony Perez, St. Leo University
Prologue
It is no secret that the number of people 65 and over in the United States is growing rapidly, a phenomenon recognized as the “graying of America” (Himes, 2001). The numbers are staggering. There has been an exponential increase in older people in the United States since 1870: from 1 million up to 52 million in 2018—a number now larger than the entire population of Canada (Mather, Scommegna, & Kilduff, 2019). During recent decades, the 65 and older group has been increasing twice as fast as the rest of the population, and adults 80 and older are the fastest-growing segment of the population globally (Hudson & Goodwin, 2013).
As a result, the U.S. population looks different than it did earlier in the 20th century. In 1900, average life expectancy at birth was 47 but is now close to 79. A hundred years ago, only 4% of the population was over the age of 65; by 2017, that figure had jumped to more than 15%. The pace of growth continued in the first decades of the 21st century, and in 2011 the huge baby boom generation—those born between 1946 and 1964—moved into the ranks of older adults. The U.S. Census Bureau projects that by 2030 the proportion of the population over age 65 will reach close to 20% and there will be at least 400,000 people who are 100 years or older. This rate of growth in the older population is unprecedented in human history. Within a few decades, one in five of all Americans will be eligible for Social Security and Medicare, contrasted with one in eight today; in 2019, 9 out of 10 persons age 65 and older received Social Security (Social Security Administration, 2019a).
We usually think of aging as strictly an individual matter. But we can also describe an entire population as aging or growing older, although to speak that way is metaphorical. In literal terms, only organisms, not populations, grow older. Still, the average age of the population is increasing, and the proportion of the population made up of people ages 65 and older is rising. This change in the demographic structure of the population is referred to as population aging (Clark et al., 2004; Olshansky, 2015; Uhlenberg, 2009).
Population aging results from two factors: The proportion of older persons in a population increases because of persons living longer (e.g., longevity), and the proportion of children in the population decreases because of lower birthrates. Both of these trends took place throughout the 20th century and have continued into the early 21st century, but the drop in the numbers of children being born is a more significant factor for population aging than is people living longer. In 1900, the United States had a relatively young population: The percentage of children and teenagers in the population was 40%. According to U.S. Census Bureau data, by 2017, the proportion of youth had dropped to 24%, an all-time low. By contrast, those ages 65 and older increased from 4% in 1900 to 16% in 2017, with larger increases still to come (Kaiser Family Foundation, 2017b). During the next several decades, overall population growth in the United States will be concentrated among middle-aged and older Americans.
The United States is not the only country undergoing population aging (Bosworth & Burtless, 1998; Cherlin, 2010; National Institute on Aging, 2007). For example, average life expectancy at birth in Japan is currently 84 years (World Population Review, 2020), the highest in the world, and the proportion of the population ages 65 and older there is 27% (World Bank, 2019). In Germany, Italy, and Japan, the population is aging because of low birthrates as well. Think of the state of Florida today as a model for population aging: a population in which nearly one in five people is already over the age of 65. We can ask: How long will it take different nations to reach the condition of “Florida-ization”? The answer is that Italy already looked like Florida by 2003, Japan by 2005, and Germany by 2006. France and Great Britain resembled Florida in 2016, whereas the United States in general will not reach “Florida-ization” until 2023.
Exhibit P.1 Life Expectancy at Birth, by Sex, Race, and Hispanic Origin: United States, 1980–2014
Source: Figure 18 in Centers for Disease Control and Prevention (2015); CDC/NCHS, National Vital Statistics System.
Note: Life expectancy data by Hispanic origin were available starting in 2006 and were corrected to address racial and ethnic misclassification.
Population aging also shows up as an increase in the median age for the entire population, that is, the age at which half the population is older and half the population is younger. The median age of the U.S. population in 1820 was only 17 years; by 1900 it rose to 23 and by 2018 to 38. It is estimated that the median age of the American population by 2030 will be 42 years. This shift is a measure of the dramatic impact of population aging.
It is clear, then, that populations age for reasons different than individuals do, and the reasons have to do with large-scale demographic trends. In the first place, population aging occurs because birthrates go down. With a smaller proportion of children in the population, the average age of the population goes up. Population aging can also come about because of increases in life expectancy—people living longer on average. Finally, the process of population aging can be influenced for a time because of the characteristics of birth cohorts. A cohort is a group of people born during a particular time who thereby experience common life events during the same historical period. For example, the cohort born during the Great Depression of the 1930s was relatively small and thus has had minimal impact on the average age of the population. By contrast, the baby boomers born after World War II are a large cohort. Because of this cohort’s size, the middle-aged baby boomers are dramatically hastening the aging of the U.S. population. Even larger than the baby boomer cohort is the Millennial or Gen Y cohort, the members of which were ages 24 to 39 as of 2020 (Pew Research Center, 2020). How will this large cohort, numbering 72.1 million, impact population aging in the U.S. in future decades?
In summary, then, trends in birthrates, death rates, and the flow of cohorts all contribute to population aging. What complicates matters is that all three trends can be happening simultaneously, as they have been in the United States in recent decades. Casual observers sometimes suggest that the U.S. population is aging mainly because people are living longer. But that observation is not quite accurate because it fails to take into account multiple trends defined by demographic factors of fertility, mortality, and flow of cohorts.
A demographic description