later 10 to 15 percent of American 7 year olds CNN 10 to 15 percent of American 7 year olds rate of precocious puberty 10 to 15 percent of American 7 year olds according to Health.com Study: More U.S. girls starting puberty early as early as age seven 10 to 15 percent of American 7 year olds CNN.com August 10, 2010 10 to 15 percent of American 7 year olds backed up those findings