If you are over 25 years old, you have much to be thankful for, as there is a very good chance you would not have advanced to your current age if you had lived in any time but the modern period.
Life expectancy from prehistoric times until 1400 or so was in the range of 20-30 years. For example, Benedictine monks in Canterbury, England in the period 1395-1505 lived, on average, only 22 years from birth, despite having better nutrition, clothing, sanitation and shelter than the population as a whole.
By the mid-16th century, life expectancy had risen to the mid-30s, on average, with substantial fluctuation from period to period. At the beginning of the 19th century life expectancy was about 37 years. A steady advance begins at the turn of the 19th century and accelerates after about 1875. After the 1860s, there is no period in which life expectancy actually declines from one period to the next.
Thus far in the 20th century, life expectancy has increased by 24 years in Sweden and by 27 years in England and Wales, typical gains for Western European countries. Italian life expectancy has gone up by 32 years, from 43 to 75, and Czechoslovakian life expectancy has increased by 31 years, from 40 to 71. U.S. life expectancy, although not as well documented as Europe’s, has mirrored the European increases.
Source: “The State of Humanity,” edited by Julian Simon, 1995.