Please provide an analysis of "After Fifty Years" by William Faulkner. What is the meaning or the theme of the poem? Explain your reasoning using literary devices as evidence.

The poem "After Fifty Years" by William Faulkner tells the story of an old woman who is alone after growing old. After fifty years of living with others, the woman in the poem finds herself utterly alone. She has an empty house and an empty heart. As a result of her loneliness, she has become lost in dreams—mostly about young men she once knew and about her beauty during her youth.
Thematically, the poem centers around the idea of the passage of time. A thematic statement that might be derived from the poem could be: fixation on loss in the past can delude the mind into self-preserving behaviors. For the woman in the poem, she focuses too much on history, rather than moving on to find something new in her life. The poem describes her situation thus:

She rose in dreams from other dreams that lentHer softness as she stood, crowned with soft hair.And with his bound heart and his young eyes bentAnd blind, he feels her presence like shed scent,Holding him body and life within its snare.

She is too lost in dreams, thinking back to her youth when her hair was soft and she was beautiful. The "softness" that the poem focuses on is the natural softness of a young person, something that would have lent itself to both attracting young men and having fun. She also focuses on young men from the past who were interested in her; in this case, she has the memory of that young man trapped—forced to live with her in her old and decrepit form.
There are a few literary devices in the poem. When the poem says:

No one save her, for still she tries to weaveWith blind bent fingers, nets that cannot hold.

This is a metaphor. The nets are metaphorical; rather than being real nets, they are "nets" of memory with which she is trying to catch hold of the things of the past, something that is impossible. Yet she still tries, and therefore no one can save her.
When the poem says:

Once all men's arms rose up to her, 'tis told,And hovered like white birds for her caress

This is an example of simile when it compares the arms of the men to birds. They are constantly reaching out for her, like birds that hover and wait for a place to land. This also could be considered imagery, because it creates a vivid image in the mind of the reader about how her past life was lived. From this description, we can imagine the kind of attention she received from these men.
Finally, when the poem says:

A crown she could have had to bind each tressOf hair, and her sweet arms the Witches' Gold.

The poem here is playing on the trope of a witch's enchantment. The "witches' gold" is her hair, and the implication is that her hair is so beautiful that it works a spell on whatever man might look at it. That is the reason that so many men fell in love with her: because of her great beauty. By comparing the beauty to a spell, it helps the reader understand precisely what she has lost in becoming old and gives some reason for why she is so obsessed with her dreams of the past.