Smith's book is usually considered to be the beginning of modern economics.
External Links
The Wealth of Nations online (http://www.econlib.org/library/Smith/smWN)
... the age of 18, 34.0% from 18 to 24, 17.6% from 25 to 44, 20.5% from 45 to 64, and 14.1% who are 65 years of age or older. The median age is 28 years. For every 100 ...