JAQUES. Last scene of all,
That ends this strange eventful history,
Is second childishness and mere oblivion;
Sans teeth, sans eyes, sans taste, sans everything (2.7.170–173).
In what is essentially a "filler" speech in act 2, scene 7 of William Shakespeare's As You Like It—used to pass the time between Orlando going offstage and returning with Adam, his aging servant—a cynical, melancholy courtier named Jaques gives a two-minute speech which is famously known as "the seven ages of man."
The speech begins with " All the world's a stage, / And all the men and women merely players" (2.7.146–147) and ends with the lines cited above.
"Second childishness," or extreme old age, is often analyzed and interpreted negatively, most often in terms of the words that follow—"mere oblivion" and "Sans teeth, sans eyes, sans taste, sans everything." Nevertheless, "childishness" can also be interpreted in terms of its alternative, positive definition of being "childlike," and as distinct from the utter helplessness and dependence on others that Jaques implies is the last stage of life.
While it's true that the youngest of children have no teeth, the same cannot be said of a child's sight, taste, or any other of its senses, through which the child discovers and experiences itself and the world around it with excitement and wide-eyed wonder.
The youngest of children also require constant care, as do some of the oldest among us, but it's not long after a child learns to speak that it demands to "do it myself." The same is true of some of the oldest among us who resent having things done for them, particularly if they believe that they're capable of taking care of themselves, even if in a limited capacity.
In his cynicism, Jaques sees these as negative qualities, in much the same way that he focuses on the negative aspects of each of the "seven ages"—the "mewling and puking" of the infant, "the whining school-boy," the "woeful ballad" of the lover, the soldier who is "quick in quarrel," seeking only the "bubble reputation," the justice who spouts profound nonsense, and the "pantaloon," the foolish old man with a "childish" voice whose tights are too big for his skinny legs.
Jacques's use of "childish treble" in describing an old person's voice is a clue to the meaning of "second childishness," a phrase Jaques uses just three lines later in the speech. This same "childishness" is exemplified by Jacques himself in the childlike excitement of discovery he feels in his "A fool, a fool! I met a fool i' th' forest" speech earlier in the same scene (2.7.12–35, 37–44).