Kuroki Yusaku (jap. 黒木優作) was a Japanese gerontologist who helped debunk the claimed age of Shigechiyo Izumi in 1984.
The September 1984 cover story on Shigechiyo Izumi was quite interesting, especially for we in Japan who use East West Journal for our English study. However, while reading this story we came across other information indicating that Izume's age is 104, not 119 as claimed by the Guinness Book of World Records. Some five years ago, the Weekly Yomiuri Magazine had raised questions about Izume's claimed birthdate of 1865. After checking was done by Kuroki Yusaku, chairman of the Japan Committee to Honor People Who Have Attained Longevity, the following explanation was offered in the December 2, 1984 issue of Yomiuri. The original family register says that Izume's marriage was reported on May 11, 1919. The town pamphlet, distributed at Izume's birthday celebration in 1979, says he married at the age of thirty-nine. That would point to a birthdate of 1880. The family register also reports that in December 1901, it was entered that, as a result of a court hearing in November (reason for hearing unknown), Shigechiyo Izume was declared the adopted son of Katsuzumi Izumi, not the real son as had been listed. Yusaku suggests that Katsuzumi's real son, born in 1865 and named Shigechiyo, later died. A baby boy was adopted and also named Shigechiyo. Since neither the real son's death nor the adoption were reported, the adopted Shigechiyo took on the first son's birthdate of June 29, 1865 in the family register. Yusaku now says that he will ask the publishers of the Guinness Book to withdraw the entry claiming Izumi to be the oldest person to ever live. The oldest Japanese now are two women of 109 years, Ine Tsugawa of Tokushima and Tsuru Ishii of Hiroshima.