The age at which mothers have children is strongly related to income prospects. A more global perspective from this graph at Gapminder, shows that as GDP per capita (income) rises the number of teen births decreases. In Africa, there is about 1 birth for every 10 women under 19 per year, while it is a little less than ½ that in the United States (.4 births per 10 women). So Gloucester was still below the national average this year.
This negative relationship between income and having children young is generally explained by if women have more prospects economically, then giving up some of those prospects through pregnancy seems less attractive. Interestingly though the US is a bit above where you would expect in terms of the number of teen pregnancies given our GDP per capita. My guess is this is due to a combination of culture, inequality, and availability of contraceptives.
h/t to broadsheet at Solon.com
Or if you prefer a map of fertility see the below.
Adolescent Fertility Rate (Births per 1,000 Women Aged 15-19)