One factor that could explain why the Baby Boomer generation is so much larger than Gen X, Gen Y, or Gen Z cohorts is the post-World War II economic boom in the United States. This period of economic prosperity and social stability led to an increase in birth rates, resulting in the Baby Boomer generation being larger in size.
As Gen Y and Gen Z cohorts age, they will continue to affect the age structure and growth rate of the United States by potentially increasing the number of older individuals in the population. Once Gen X reaches retirement age (65+), this will likely lead to a shift in the age structure as more individuals from Gen X move into the older age categories, potentially impacting the workforce and social services for older adults.