How is taking in a sail linked to growing old?

In the poem "Terminus" by Ralph Waldo Emerson, the poet begins by stating that "it is time to be old, to take in sail." The connection between these two concepts can be perceived once we recognize the extended metaphor Emerson uses in this poem to discuss the journey of human life.
In this metaphor, made explicit in the final stanza, the speaker is a sailor on the "storm of time." He is responsible for manning his own vessel ("I man the rudder, reef the sail"). The seas themselves are not under the speaker's control, but they are ordained by the "god of bounds." We can understand this as a representation of how a person may have free will and make his own choices in life while not always being able to control his own ultimate fate or destiny, which is ordained by a higher power. At this juncture of the speaker's life, Emerson says, "the port . . . is near," and the seas are no longer stormy: the speaker has traversed the stormiest parts of life and is reaching his old age, where "every wave is charmed." As such, he may bring in the sail on his metaphorical vessel because it is now time to dock the boat and rest. Emerson is suggesting that death is near and that this will be the sailor's due reward.