Noncitizens Under Age 35: 2010–2012

"According to the 2010-2012 American Community Survey, 10.3 million noncitizens under age 35 lived in the United States, representing less than 4 percent of the total U.S. population. Most of these immigrants - 80 percent- were young adults between the ages of 18 and 34. About three in five  lived in this country for 5 years or longer, and over half arrived when they were under age 18..."
Noncitizen population

Noncitizen Eligibility for Federal Public Assistance: Policy Overview and Trends

"The extent to which residents of the United States who are not U.S. citizens should be eligible for federally funded public aid has been a contentious issue for more than a decade. This issue meets at the intersection of two major policy areas: immigration policy and welfare policy. The eligibility of noncitizens for public assistance programs is based on a complex set of rules that are determined largely by the type of noncitizen in question and the nature of services being offered. Over the past 16 years, Congress has enacted significant changes in U.S. immigration policy and welfare policy. Congress has exercised oversight of revisions made by the 1996 welfare reform law (the Personal Responsibility and Work Opportunity Reconciliation Act, P.L. 104-193)— including the rules governing noncitizen eligibility for public assistance that it established—and
legislation covering programs with major restrictions on noncitizens’ eligibility (e.g., food stamps/SNAP, Medicaid)."
http://www.fas.org/sgp/crs/misc/RL33809.pdf

Noncitizen Eligibility for Federal Public Assistance: Policy Overview and Trends
"The extent to which residents of the United States who are not U.S. citizens should be eligible for federally funded public aid has been a contentious issue for more than a decade. This issue meets at the intersection of two major policy areas: immigration policy and welfare policy. The eligibility of noncitizens for public assistance programs is based on a complex set of rules that are determined largely by the type of noncitizen in question and the nature of services being offered.
Over the past 15 years, Congress has enacted significant changes in U.S. immigration policy and welfare policy. Congress has exercised oversight of revisions made by the 1996 welfare reform law (the Personal Responsibility and Work Opportunity Reconciliation Act, P.L. 104-193)—including the rules governing noncitizen eligibility for public assistance that it established—and legislation covering programs with major restrictions on noncitizens’ eligibility (e.g., food
stamps/SNAP, Medicaid).

This report deals with the four major federal means-tested benefit programs: the Supplemental Nutrition Assistance Program (SNAP, formerly food stamps), the Supplemental Security Income (SSI) program, Temporary Assistance for Needy Families (TANF) block grant programs, and Medicaid. Laws in place for the past 15 years restrict the eligibility of legal permanent residents (LPRs), refugees, asylees, and other noncitizens for most means-tested public aid. Noncitizens’ eligibility for major federal means-tested benefits largely depends on their immigration status;
whether they arrived (or were on a program’s rolls) before August 22, 1996, the enactment date of P.L. 104-193; and how long they have lived and worked in the United States.."

Treatment of Noncitizens in H.R. 3200
"This report outlines the treatment of noncitizens (aliens) under H.R. 3200, America’s Affordable
Health Choices Act of 2009. In particular, the report analyzes specific provisions in H.R. 3200,
and whether there are eligibility requirements for noncitizens in the provisions. Within the bill,
noncitizens are treated differently in several provisions. In 2008, there were approximately 37.3
million foreign-born persons in the United States. The foreign-born population was comprised of
approximately 15.1 million naturalized U.S. citizens and 22.2 million noncitizens.

H.R. 3200 includes an individual mandate to have health insurance, with tax penalties for
noncompliance. Individuals who do not maintain acceptable health insurance coverage for
themselves and their children would be required to pay an additional tax. Some individuals,
including nonresident aliens, would be exempt from the individual mandate. “Nonresident alien”
is a term under tax but not immigration law. For federal tax purposes, alien individuals are
classified as resident or nonresident aliens. In general, an individual is a nonresident alien unless he or she meets the qualifications under a residency test. Thus, legal permanent residents, and noncitizens and unauthorized aliens who qualify as resident aliens (i.e., meet the substantial
presence test), would be required under H.R. 3200 to have health insurance..."