The Child is father of the Man - the boy is the type of the man

William Wordsworth wrote:

My Heart Leaps Up When I Behold'

My heart leaps up when I behold
A rainbow in the sky:
So was it when my life began;
So is it now I am a man;
So be it when I shall grow old,
Or let me die!
The Child is father of the Man;
And I could wish my days to be
Bound each to each by natural piety.

Similarly 

• "The boy is the type of the man" 2T312
• “Bienaventurado el que fue joven en su juventud” Chejov, “El corresponsal”