Average life expectancy at birth for English people in the late 16th and early 17th centuries was just under 40 – 39.7 years. However, this low figure was mostly due to the high rate of infant and child mortality; over 12% of all children born would die in their first year. A man or woman who reached the age of 30 could expect to live to 59. Life expectancy in New England was much higher, where the average man lived to his mid-sixties and women lived on average to 62.The first thing to note about this is its very high 'oh my GOD!' quotient. That's astonishing. In the 16th and 17th centuries, 60 out of 100 children died before they reached adulthood. There's nowhere in the world today that has anything like that -- not Somalia, not Afghanistan (the current world-leader in infant mortality rates, with 121 deaths per 1000 live births) (compare the UK's 4.5), nowhere. It was a holocaust.
Demographers estimate that approximately 2% of all live births in England at this time would die in the first day of life. By the end of the first week, a cumulative total of 5% would die. Another 3 or 4% would die within the month. A total of 12 or 13% would die within their first year. With the hazards of infancy behind them, the death rate for children slowed but continued to occur. A cumulative total of 36% of children died before the age of six, and another 24% between the ages of seven and sixteen. In all, of 100 live births, 60 would die before the age of 16.
Family Size. An English woman who married at the average age of 23 ½ could expect a reproductive span of about 20 years. In New England, where women typically married at 20 or 21, the potential years for giving birth increased by those two or three years. The typical English woman would give birth six or seven times. [Plimoth Plantation Faculty, 'Raising Children in the Early 17th Century: Demographics' (pdf)]
What about subsequently? Well rates stayed stubbornly high until the end of the nineteenth-century:
Toward the end of the 19th century, before the wide-spread recognition that bacteria was a major cause of illness, rates of infant mortality throughout the world were much higher than they are today. It was common for 20% or more of all infants in many populations to die before they reached their first birthday, and often mortality rates were even higher for children between the ages of one and five. In the last years of the 19th century, large areas of Russia had an infant mortality rate of nearly 28%. In 1901, the infant mortality rate in England, birthplace of the industrial revolution and capital of a global empire, was 16%. By 1930 the number of infant deaths had declined dramatically in many countries as the causes of infection came to be understood. Most progress up to this point was due to precautions such as hand washing and sterilization of milk rather than to actual medical advances, since antibiotics and sulfa drugs—the first medications that were really effective in fighting infection—were not developed until the late 1930s and 1940s. Although data on infant mortality in the developing nations is much less complete than the figures for the developed world, it is clear that the world's poorer countries have made dramatic progress in lowering infant mortality in the 20th century, due in large part to public health programs, especially those that have combated malaria through mosquito control. Availability of medication and immunization have also played a major role in improving infant health in developing nations.
In 1993 the infant mortality rate worldwide was 69 deaths per 1,000 live births, according to figures released by the United Nations Population Fund (the U.S. Census Bureau figures are slightly lower). The U.N. also reported an average infant mortality rate for the world's industrialized nations of 12 deaths per 1,000 live births. According to the U.S. Census Bureau's World Population Profile, the highest ratio of infant deaths (177 per 1,000 live births) was found in the Western Sahara and the lowest (four per 1,000) in Japan. The 1993 infant mortality rate in the United States was 8.4 per 1,000, ranking it twenty-second among the world's developed nations (a rank it maintained over the following two years, according to preliminary data for 1994 and 1995). The relatively high rate of infant deaths in the U.S. compared to Japan and Western Europe is largely accounted for by high infant mortality rates among low-income minority populations. [Thomson Gale, 'Infant Mortality' (1998)]