Chagnon

In this thread Age of conception in pre-history? - boards.ie an argument is made that in prehistoric times women would concieve for the first time typically at about 17 and that because of this men have evolved preferences for girls under this age. Is the reasoning right?

What was probably the typical age a woman would conceive for the first time in prehistoric times before contraception etc? I know there would have been some variations between tribes living in different areas, but I'm only after a likely average.