According to a study published by Dr. Myrna Weissman, only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four.
(A) only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four
(B) only one percent of Americans born before 1905 suffer major depression by the age of seventy-five; if they are born since 1955, six percent become depressed by age twenty-four
(C) of Americans born before 1905, only one percent of them have suffered major depression by age seventy-five, but six percent of those born since 1955 do by the age of twenty-four
(D) major depression is suffered by the age of seventy-five by only one percent of Americans born before 1905, and by age twenty-four by the six percent born since 1955
(E) Americans born before 1905 suffer major depression by the age of seventy-five only one percent of the time, but six percent of those born since 1955 did so by age twenty-four

Meaning Analysis:
This sentence presents 2 findings of a study.
Finding 1: Group = Americans borns before 1905. Only 1% of this group had suffered major depression by the age of 75.
Finding 2: Group = Americans borns since 1955. 6% of this group had become depressed by the age of 24.

Error Analysis:
1: According to a study published by Dr. Myrna Weissman, only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five;
2: Of those born since 1955, six percent had become depressed by age twenty-four.

Subject-Verb = No Errors
Verb Tense = Both clauses use past perfect tense correctly. The author shows two events in both findings:
Event 1: People become depressed
Event 2: People become certain age
For example finding 1 states that 1% of people already became depressed by the time they turned 75 years.
Similarly finding 2 states that 6% of people were already depressed by the time they turned 24 years.

Thus clearly, the author intends to state that the event of becoming depressed happened before the population turned the specified age. Thus, there is an intended sequencing of events in the past time frame and hence the use of past perfect tense is appropriate. Note carefully here that the latter past event is expressed using time phrase "by the age of 75" or "by the age of 24".
Modifiers = "According to a study..."correctly modifies the findings of the study that follow.

This sentence is correct as-is.

POE:
(A) only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four
Correct as-is

(B) only one percent of Americans born before 1905 suffer major depression by the age of seventy-five; if they are born since 1955, six percent become depressed by age twenty-four
Incorrect. This choice changes the intended meaning of the sentence. This sentence appears to indicate the findings as facts that are true as general practice. For example, If one is born is December, he is poised and very hardworking. On similar lines Choice B indicates that if people are born since 1955, 6% become depressed by age 24. This is non-sensical since the findings stated in the sentence are a one time finding. We cannot have a repeat instance of people being born before 1905 or since 1955.

(C) of Americans born before 1905, only one percent of them have suffered major depression by age seventy-five, but six percent of those born since 1955 do by the age of twenty-four
Verb Tense: "present perfect - have suffered" is non-sensical since the action of suffering is complete. This action got complete when people turned the age 75.
Redundancy: Of Americans, only 1% of them

(D) major depression is suffered by the age of seventy-five by only one percent of Americans born before 1905, and by age twenty-four by the six percent born since 1955
Verb Tense : Simple present tense is incorrect (it is in passive voice in this choice) as explained in Choice B
Connecting List: The choice uses following list structure:
Major depression is suffered
1: by the age of 75...
2: by age 24
The second element is connected using ,and. It should be connected using only 'and'.
Awkward Construction: Passive voice makes this sentence overly complicated and unclear.

(E) Americans born before 1905 suffer major depression by the age of seventy-five only one percent of the time, but six percent of those born since 1955 did so by age twenty-four
Verb Tense : Simple present tense is incorrect as explained in Choice B.
Meaning: 1% People suffer from depression is not same as People suffer from depression 1% of the time. Thus, this choice changes the intended meaning of the sentence.

Thanks,

Payal