After 114-year-old German man Gustav Gerneth's death on 22 October 2019, Watanabe was the oldest known living man in the world, and credited his longevity to laughing often, forgetting bad things and not to get angry, and said he wanted to try his best to eat delicious healthy food until age 120 and might eat his own food except hard food and liked sweet food. He was recognized as the world's oldest living man by Guinness World Records on 12 February 2020. He died just eleven days later, at 11:10pm local time the evening of 23 February, just eleven days before his 113th birthday, and was succeeded as the oldest living man by Englishman Robert Weighton.