I have to reject your premise, as death from old age is not recognized by biology. However, to answer your question, we have to look at survival rates to age 65. We see in table 3.1 of "65+ in the United States" that the first time 50% of people reached 65 was 1920ish.

source: http://www.census.gov/prod/1/pop/p23-190/p23-190.pdf