Life expectancy is no exact science. There is no guarantee for anything; there is only a chance for it. Some persons for no known reasons reach well into old age, topping 90 and even 100 yrs old. Most of us cannot expect to reach this level of “ripeness”, however with proper diet, exercise and a little luck in genetics, persons suffering no great injuries or ailments can expect to live to fairly old ages.
Life expectancy over the centuries has risen greatly. There were actually two levels of expectancy in earlier centuries. Childhood disease often shortened ones” life span considerably, and so at birth you would have a fairly short life span expectancy that would be increased after reaching the milestone of mid-teens.
During the 13th century life expectancy after 15 yrs of age ranged from the early 40’s to the early 60,’s, the following century however, the life expectancy was lowered to only 55 due to the Black Death (Bubonic plague) that took millions, nearly half of the population of Europe succumbed to this dreaded disease. Thought long gone, this disease has actually had several reported cases throughout the world in recent years.
The centuries following the Black Death saw a rise in human life expectancy after 15, increasing from the fairly young age of 55 to as high 69 or 70 yrs of age, and then increasing slightly more to 71 years of age the following century. These numbers are considered the highest age possible, in reality people usually didn”t live much beyond 30 or 40 yrs of age due to various illnesses, even the flu that we see as a nuisance for about a week every year killed millions.
The average life expectancy in the early American colonies was a mere 25 yrs of age, and in New England 40% of children never reached maturity. The industrial revolution in England saw the average number of childhood deaths of children under the age of five years decrease from approximately 75% mortality rate to about 30%.