Slavery was abolished in the USA in 1865, and the interviews were carried out in 1936 to 1938. Thus, all of the interviewees were at least 70 years old (or else they couldn't have been slaves in the US). Over 2/3 of the interviewees were over 80, and some over 100.

The age distribution of the interviewees was:

Age bracket	Percentage
1-5	16
6-10	27
11-15	24
16-20	16
21-30	13
31+	3

The over-30s, approximately 70 people, (and some of older interviewees in the 21-30 bracket, depending on when they were interviewed) would have been over 100 years old when interviewed. Most of the interviewees were under 16 years old when slavery ended, as the younger people were more likely to still be alive to be interviewed.

Reference:

The age distribution is from, and more details about the project can be found in:

• Yetman, N. (1967), "The Background of the Slave Narrative Collection", American Quarterly 19(3), 534-553. https://doi.org/10.2307/2711071 https://www.jstor.org/stable/2711071