[Excerpt] By 2035, the growing number of beneficiaries due to the aging of the baby-boom generation will cause scheduled spending to climb to 6.1 percent of GDP, CBO estimates. However, there is uncertainty inherent in CBO's projections; in 10 percent of the simulations, outlays in 2035 are below 5.3 percent of GDP and in 10 percent they exceed 7.3 percent of GDP. In most simulations, outlays in 2035 are projected to account for a much larger share of GDP than the share in 2010.