How many us kids are virgins at 20?

About 13%: According to data from the national center for health statistics, 2006 - 2008, 12% of women and 13% of men ages 20-24 said they were virgins.

Here are some refs: Here are some good references: http://goo.Gl/izmnc (30 to 35% of U.S. Teens claimed to have had sex by age 19). Here's a nice graph http://goo.Gl/es0le (15% of men and 24% of women have sex for the first time at age 20 or older).