Why is William Faulkner's poem "After Fifty Years" a good poem? Why does it work? How does he use his sonnet to truly make readers feel like what it would be to be fifty years older?

Faulkner's poem "After Fifty Years" focuses on the relationship between aging and loss of love.
Faulkner emphasizes the passage of time through the tense shifts that happen after the fourth and eleventh lines. The poem opens with the present tense, showing the subject of the poem as she is now:
Her house is empty and her heart is old.
Faulkner is directly telling us that part of her is old. The heart being old suggests that her heart has been through a lot, which suggests the passage of time. The phrase "still she tries to weave / with blind bent fingers" features three alliterations that help suggest time gone by; older bodies are more likely to be blind and bent, and the word "still" tells us that an action is being repeated.
The poem then shifts to past tense as Faulkner tells us what "once" was. The tense shift highlights the idea of then versus now. The phrase "'tis told" makes this feel like an ancient tale that has been repeated and spread around. "A crown she could have had" makes us think of what might have been.
The poem shifts back to present tense for the last three lines, again highlighting a change in time. Notice how "blind" and "bent" are repeated, this time describing "his young eyes." Her heart is called old, while his eyes are young. This puts him at a contrast to her, further showing that the main character is older and has experienced a passage of time.