All the world's stages are made of wood.

"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" II.vii.32.

Hey, Mr. Costello, I found an extended metaphor!  Oh, and not only that, but it is also ironic.  It's ironic, because the character telling us that the whole world is a stage, is on a stage, where all the men and women (well, mostly men since there were never actresses in Shakespeare) were legitimately players who exited and entered.

This metaphor is one of the most famous monologues in history from what I have learned, so I have two questions:

1. Why Jaquez?
2. Why in As You Like It?

To this point in the play, Jaquez has mostly been portrayed  as a merciful person who sees the worth in everything.  He cried when a deer died, obviously he believes that everything is equal.  Before this monologue, there was talk about death and elders.  It makes sense in context that Jaquez would be the one that is honored to give this monologue about the evolution of ages.

I think it may have been in this play since it was Shakespeare's last comedy.  Not only does this monologue explore the idea of death, but it also talks about equality and importance in variety.  Shakespeare seems to make it clear that he does not want to write comedies with a bang.