Final answer:
As of 2013, the Census Bureau reported that 20% of the U.S. population was over 60 years old, indicating a notable demographic shift over the past century.
Step-by-step explanation:
The student's question pertains to the demographic shift in the U.S. population, particularly the increase in the number of people in the over-60-year age group. According to the Census Bureau reports, as of 2013, 20% of the U.S. population was over 60 years old. This indicates a significant change when compared to historical data which showed that in 1900, only about 4 percent of the total population was over sixty-five years old. This change is reflective of broader trends such as increased life expectancy and the aging of the Baby Boomer generation.