He was a Japanese supercentenarian and, according to Guinness World Records, became the person with the greatest authenticated age in the world after the death of Marie Laure du-Serre-Telmon. Assuming his claimed birth-date is correct, he would have attained an age of 120 years, 184 days, older than any other recognized male, and be the second-longest lived human ever, second only to Frenchwoman Jeanne Calment. He also holds the record for the longest working career for a person, spanning 98 years. He was recorded as a six-year-old in Japan's first Census of 1871. His wife died at the age of 90. He drank shōchū (a Japanese alcoholic beverage distilled from barley), and took up smoking at age 70. He began his career in 1872 goading draft animals at a sugar mill, and retired as a sugarcane farmer in 1970 at the age of 105. He attributed his long life to "God, Buddha and the Sun." He stood at 1.42 meters (four feet, eight inches) tall, weighed 42.6 kilograms (94 pounds) and lived through 71 Japanese Prime Ministers; his life spanned five Emperors of Japan from Komei Tenno to Showa Tenno and five nengo from Keio at the close of the Edo era to near the end of the Showa era.
He died of pneumonia after a brief hospitalization at 12:15 GMT, the same day as Jeanne Calment's 111th birthday. He was 120 years and 184 days old (if the 1865 birth year is correct), the last recognized surviving person of the 1860s, one of only two men to reach the age of 116 (along with Jiroemon Kimura, also from Japan) and the longest holder of the "oldest living person" title. He had outlived the only other supercentenarian born in the year 1865, who was also the oldest living woman - Alice Coles (who was 8 days younger than Izumi, having been born August 28, 1865) - by 8 years, with Coles having died in 1978.
Following his death, Augusta Holtz became the oldest living person. For more than 20 years after his death every person with the title of the world's oldest living person was female until Emiliano Mercado del Toro became the world's oldest living person on December 11, 2006.
Izumi's stated birthdate is June 29, 1865, however as Japan did not adopt the Gregorian calendar until January 1, 1873 his age appears inflated by 12 days. One of his 120 years was in fact 12 days shorter: the year 1872. His date of birth June 29, 1865 would be July 11, 1865 in Gregorian countries. This assumes that his date of birth has not been otherwise adjusted as no mention of this anomaly is made in the source. However, the actual birthdate of Izumi is August 20, 1865 - his adoptive parents (who were his grandparents) changed his birthdate from August 20 to June 29, which is considered a "luck day" - therefore making him 120 years, 184 days old rather than 120 years, 237 days old.