On 10 May 2015, following the death of 108-year-old Setsuo Ojima of Ōita City, he became the oldest living man in Ōita Prefecture, at the age of 108.
On 25 August 2016, following the death of 114-year-old Mitsue Toyoda, he became the oldest living person in Ōita Prefecture, at the age of 109.
On 2 October 2017, at the age of 110 years, 232 days, he surpassed the final age of Hajime Fujita (1902–2012), becoming the oldest man ever in Ōita Prefecture. In February 2018, he became the first man in Ōita Prefecture to reach the age of 111.
Upon his death, an anonymous lady from Hiji (who was 2 days younger than Ōya) became the oldest living person in the Prefecture, and Goro Danjo succeeded him as the oldest living man in the Prefecture.
His age was verified by Japan’s Ministry of Health, Labour, and Welfare (MHLW), as well as Ryohei Asano, and validated by LongeviQuest on 26 June 2023.