In their study, Gavrilov and Gavrilova first used Social Security data to locate 240 men born in 1887 who lived to be at least 100.They concluded that trim farmers with more than three children were more likely to live to see 100 than overweight city boys without kids. In fact, living on a farm "more than doubled a man's odds of living into the triple digits."
In 171 of those cases, the men's physical and social attributes at age 30 were recorded on their WW I draft cards -- giving the researchers a snapshot of their lives at the time.
The Chicago team then compared that data against draft card information for a randomly selected group of American men who were also born in 1887 but who did not reach 100. [Link]