Answer: D) At midlife.
Step-by-step explanation: In the given passage from "Sonnet XIX" by John Milton, the speaker is in his late life, he thinks his life is ending and he is remembering how he has spend half of his life without being able to see ("...in this dark world and wide"), we know that he lost his vision at midlife because he expresses it with the phrase "Ere half my days" and then he lost his talent.