Thanks for your observation, your point about infant mortality is valid... I remember seeing somewhere that decreasing infant deaths is a large part of the increase in average life expectancy.
However, I do not think this accounts fully for the drastic and considerable increase in average lifespan.
Info On Infant Death:
The infant mortality rate in the United States has dramatically decreased from a level of 47 per 1000 live births in 1940 to 7.7 deaths per 1000 live births in 1996. This reduction is due to advances in prenatal care, care during delivery, and management of complications existing after delivery. Also, many infectious diseases that used to claim the lives of many infants have been eradicated or controlled. The education of women of childbearing age concerning pregnancy and the widening availability of health care in this country have also played a role in this statistic.
BobDrake has posted this article in the following topic link
----From the moment of birth, we begin the battle against the inevitable. Statistics say that a newborn child can expect to live an average of 76 years. But averages may not be what they use to be.
In 1796, life expectancy was 24 years. A hundred years later it doubled to 48. Right now, it's 76. "Over half the baby boomers here in America are going to see their hundredth birthday and beyond in excellent health," says Dr. Ronald Klatz of the American Academy of Anti-Aging. "We're looking at life spans for the baby boomers and the generation after the baby boomers of 120 to 150 years of age."