Answer:
Compares the "ashes of youth" to a "youth"
Explanation:
In these lines, the author tends to compare himself to the glowing remnants of a fire, which lie on the ashes that once let it burn; it will be extinguished as it sinks. It reveals that the youthful life is gone as ashes which happens to bring one on the deathbed. Therefore, it's comparing the life of a youth as ashes of youth which is gone as one on their deathbed which means inevitable death.
This is from Sonnet 73 by William Shakespeare.
