Lohman says she also has data collected in 2006 from the same subjects, who were between 16 and 20 by that time.
Taylor, co-author of two medical anatomical papers about the foreskin, explains the latest research at the website.
We know from our follow-up interviews that one boy who reported having sexual intercourse for the first time at age nine had fathered four children by the time he was 18.