I think that's because the statistics are typically reported in age-group cohorts, so people 'in the know' tend to think of it as pregnancies from age 13-15, pr

I think that's because the statistics are typically reported in age-group cohorts, so people 'in the know' tend to think of it as pregnancies from age 13-15, pregnancies from age 15-17, pregnancies from age 17-19. At least, that'd be my guess because when I was doing research on teenage crime rates, the government statistics that I found initially were all expressed as such and I didn't have access to the raw data.