One social factor that could explain why the Baby Boomer generation is so much larger than the Gen X, Gen Y, and Gen Z cohorts is the post-World War II baby boom, where there was a significant increase in birth rates in the United States. This was due to economic prosperity, as well as a cultural emphasis on family values during that time.
Gen Y and Gen Z are projected to have a major impact on the age structure and growth rate of the United States as they represent a large portion of the population. As Gen X reaches retirement age (65+), there may be a shift in the age structure with an increase in older individuals and potentially slower population growth rates. Additionally, there may be increased pressure on social security and healthcare systems as more individuals from Gen X enter retirement.