This phrase is now probably a cliche but was written by Shakespeare (a monologue spoken by Jacques in As You Like It). The original lines from the play are here:
All the world’s a stage,
And all the men and women merely players:
They have their exits and their entrances;
And one man in his time plays many parts,
His acts being seven ages. At first the infant,
Wants to know all the seven ages (stages)? Get a copy of the play or do a google or wiki search and read on.
But for me, that ends my quest on the Shakespearean country.
I am going to turn over a leaf on books about Ireland to prepare my travel soon.