Recent immigration has had only a tiny impact on the nation’s age structure. If the nearly 14 million immigrants who arrived in 2000 or later are excluded, it raises the average age in the United States in 2010 from 37.4 years to 37.6 years — roughly two months.
You can check out the Census Bureau data here--U.S. Census Bureau Projections Show a Slower Growing, Older, More Diverse Nation a Half Century from Now
The ACS and CPS can be used to provide insight into the impact of immigration on the size of the U.S. population. Table 6 reports six different methods using the 2010 ACS and CPS to estimate the effect of immigration on U.S. population growth since the last census. The first column in the table shows that between April 2000 (the control data for the Census) and July 2010 (the control data for the ACS) the U.S. population grew 27.9 million. The first three rows of Table 6 use the number of immigrants who arrived in the United States in the last decade to estimate the impact of immigration on U.S. population growth. As already indicated, in 2010 13.9 million immigrants indicated that they had entered the country in 2000 or later. Because those who arrived in the first three months of 2000 should already have been counted in the 2000 census we reduce this figure by 390,000, or three months worth of new immigration, to account for those who arrived in the first quarter of 2000. It is reasonable to view the 13.47 million immigrants who arrived over this time period as the basis for estimating immigration’s effect on population growth because this flow reflects current U.S. immigration policy — both legal immigration and the level of resources devoted to controlling illegal immigration.
