Jacques’ set piece here is almost a lesson to actors, as he compares the stages of Man’s (male) maturation, by making use of three devices that are available to the actors:  physical changes, clothing changes, and changes in social status.  The physical changes begin in infancy (mewling and puking), to middle age (fair round belly), to the famous list of losses in old age—teeth, hair, etc.; the clothing and props changes begin with the satchel of the schoolchild, to the slippers and pantaloons of old age; the social changes, from schoolboy thru solder and justice to second childhood.  The details of each age act like synecdoches (a detail standing for the abstract totality)—beard, spectacles, etc.—each detail a stage prop or costume piece to make the character immediately recognize to the (theatre or social) spectator.  While it is tempting to say that this poem is independent of the play, and just dropped into it like classical  Spanish Golden Age plays’ habit of inserting poems in the middle of the dramatic development, this speech is well within Jacques’ character in this play—playful, comically philosophical, verbose.  The actual progression through the seven "ages" serves as the structure for the speech.