All three projection scenarios show that, by 2020, Missouri's pyramid will have a rectangular cast. Baby boomers will swell upper sections of the pyramid to unprecedented widths, and long-sustained low levels of fertility will produce consistent narrow bands in the lower half of the pyramid. The size of the under-five age group shrank from 11 percent of the state's total population in 1960 to 7 percent in 1990. It will shrink to just over 6 percent in 2020, to 359 thousand children fully 100 thousand fewer than in 1960. The 5-13 age group also declined dramatically between 1960 and 1990, falling from 17 to 13 percent of the total population.
Gradual decline is projected over the next thirty years.
By 2020, this age group will account for 11 percent of the total population, and number about 650 thousand children 90 thousand fewer than in 1960. The 14-17 age group is somewhat larger than it was in 1960, numbering 275 thousand persons today. It will increase to about 312 thousand in the year 2000, then gradually fall to 294 thousand persons in 2020, when it will comprise 5 percent of the total population. It now numbers 520 thousand people and comprises 10 percent of the total population. It will grow to 545 thousand people in 2005, then decline to about its current size in 2020.