4 An additional factor that may come as a shock to some is how the United States has aged from 1900 to today. In the beginning of the twentieth century, half of the population was under the age of 23. When compared to data from the 2000 census which shows that half of the population in modern times is over the age of 35, a difference of 12 years, a substantial shift in ages can be seen. Some of this change has been influenced by improvements in health care, and some has been the result of fluctuations in the birthrate over the course of the century. Birthrates were initially lower at the beginning of the century, “booming” immediately after World War II, and tapering off again in the last half of the century. In fact, the “baby boom” generation not only impacted birthrates from the 1940s to the 1960s, it also affected age when measured in five-year increments. In both the beginning and middle of the century, the largest age group of U.S. citizens was under the age of five. In contrast, due to the impact of the baby boom generation, the 2000 census documented that the two largest, five-year age groups were over the age of 30: from 35-39 years of age and 40-44 years of age.
14. The author mentions the “‘baby boom’ generation” in paragraph 4 because they