One social factor that explains why the Baby Boomer generation is much larger than Gen X, Gen Y, or Gen Z cohorts is the post-World War II baby boom. This period of increased birth rates in the United States was due to economic prosperity, the return of soldiers from war, and changing social norms promoting larger families.
As Gen Y and Gen Z cohorts continue to grow and enter the workforce, they will likely impact the age structure and growth rate of the United States by contributing to a larger working-age population. Once Gen X reaches retirement age (65+), there may be a shift in the age structure as this cohort moves out of the workforce and into retirement, impacting the labor force participation rate and potentially leading to changes in economic productivity.