A quote from a letter by Benjamin Vaughan to Benjamin Franklin, 1783:

Influence upon the private character, late in life, is not only an influence late in life, but a weak influence. It is in youth that we plant our chief habits and prejudices; it is in youth that we take our party as to profession, pursuits and matrimony. In youth, therefore, the turn is given; in youth the education even of the next generation is given; in youth the private and public character is determined; and the term of life extending but from youth to age, life ought to begin well from youth, and more especially before we take our party as to our principle objects.

From The Autobiography of Benjamin Franklin, pp. 56-57.