This is a beautiful quote often mis-associated with Benjamin Franklin. Maybe, he was remembered for tidying up the original clunky version by G. Stanley Hall:

"Gross well says that children are young because they play, and not vice versa; and he might have added, men grow old because they stop playing, and not conversely, for play is, at bottom, growth, and at the top of the intellectual scale it is the eternal type of research from sheer love of truth.: