Statistics on tattoo prevalence are quite thin, and I have not found a source for systematic, historic data. I’ve found no forecasts.

1936 – 10 million Americans, 6% of population had at least one tattoo*
(Life Magazine)

2000 – 15%, ~40 million Americans**
(National Geographic News, April 2000)

2002 – 13% (1/8) of Americans
(Esquire Magazine, March 2002)

2004 – 24% of Americans
(Laumann and Derick, 2006)

2003 – 16%
2008 – 14%
2012 – 21%
(Harris Polls)

2010 – 23%
(Pew Research, Febrary 2010)

*Haven’t been able to find this figure in the 1936 Life Magazine, but they did publish an estimate of 1/10th of Americans being tattooed. Source below. Via The Vanishing Tattoo

**Unable to find this figure, although I searched the April 2000 issue of National Geographic Magazine. Via The Vanishing Tattoo

Original sources

Life, December 21, 1936. “One Out of Ten Americans is Tattooed.” P.30.

Anne Laumann, Amy Derick. 2006. “Tattoos and body piercings in the United States: A national data set.” Journal of American Academy of Dermatology, 55(3).

Pew Research Center. February 2010. “Millennials: A Portrait of Generation next.”

The Harris Poll. February 23, 2012. “One in Five U.S. Adults Now Has a Tattoo.”