Forty is the old age of ...

Forty is the old age of youth; fifty the youth of old age.
Forty is the old age of youth; fifty the youth of old age.

Quotes from the same author

An invasion of armies can be resisted, but not an idea whose time has come.
Life is the flower for which love is the honey.
I dislike wealth and prosperity, especially that of other men.
God has made the cat to give man the pleasure of caressing the tiger.
A mother's arms are made of tenderness and children sleep soundly in them.