Understanding the argument -
Researchers have concluded from a survey of people aged 65 that emotional well-being in adulthood is closely related to intimacy with siblings earlier in life. - Researchers conclude that "emotional well-being in adulthood" is closely related to "intimacy with siblings earlier in life." This statement categorically mentions "intimacy," and that rules out that just having a sibling is not enough.
Those surveyed who had never had any siblings or who said that at college age they were emotionally distant from their siblings were emotionally less well adjusted at 65 than were those who had been close to at least one brother or sister. - This premise further strengthens that "just having a sibling" is insufficient. What they need for "emotional well-being in adulthood" is "INTIMACY" with their sibling.
Option Elimination - Inference
(A) some people who attended college as young adults are likely, as a result, to be emotionally better off at age 65 - "people who attended college as young adults are likely to be emotionally better" is out of the scope of the argument. Our scope is limited to "intimacy with sibling" and its connection with "emotional well-being in adulthood."
(B) the emotional well-being of people aged 65 depends on the emotional well-being of their siblings - Out of scope.
(C) it is closeness to siblings rather than just having siblings that is more relevant to people’s emotional well-being at age 65 - OK.
(D) people who are emotionally well off at college age are more likely to be emotionally well off at age 65 as well - This option goes very far. It states that "people who are emotionally well off at college age" are 100% guaranteed that "they are more likely to be emotionally well off at age 65 as well." The argument has mentioned college in the context of "intimacy with siblings." But this option takes familiar words and creates a sound distortion.
(E) intimacy with siblings is more important to people at college age than it is at age 65 - This comparison is out of scope.