Scott,
Just in the interests of truth and accuracy, 18 year old women who have never had sex are not rare.
I don't know what the current numbers are, but as of 1995, about 50% of 19 year old women had never had sex.
N C H S - 1997 News Release - Teen Sex Down, New Study Shows
For 2006, the numbers are:
"53% of girls 15 to 19 and 49% of boys reported that they had had intercourse."
Study Suggests Shift in Teen Sex Practices - Los Angeles Times
One reason that more girls than boys have had intercourse is that older men are more likely to seek them out. All the same, as you can see, 47% of 19 year old women have never had intercourse. That's a lot of virgins.