TOKYO, JAPAN | Japanese 89-year-old Tomiji Suzuki started coding in retirement and is now making apps for the fast-growing elderly demographic, using ChatGPT to fine-tune his skills.

So far Suzuki has developed 11 free iPhone apps to help Japan's ageing population, including his latest: a slideshow of items to remember when leaving the house, from a wallet and hearing aids to patient registration cards.

He was inspired to create the app, which features his granddaughter's voice, after he realised he had forgotten his dentures as he was about to board a bullet train.

"These kinds of things happen to the elderly," he laughed, telling AFP that his age has been an advantage when coming up with ideas for the programmes.

"No matter how hard they try, I don't think younger people understand the elderly's needs and expectations," he said.

Nearly a third of Japan's population is aged 65 and above, making it the world's oldest country after tiny Monaco, and one in 10 people are octogenarians.

As in other developed economies, the plummeting birth rate has raised fears of a looming demographic crisis with not enough workers to support the growing ranks of retired.

Suzuki used to work at a trading house but developed an interest in computing in later life, taking a programming course in the early 2010s.

"I like creating things," he said.

"When I discovered I could develop apps myself -- and if I do, Apple will market them worldwide, just like that -- it felt like a great idea."

- ChatGPT mentor -

To help him make the app "Outing Prep Voice Slide Show", released in April, Suzuki asked around 1,000 coding-related questions to ChatGPT.

He described the generative AI chatbot as a "great teacher" and has even published a book about using it as a programming mentor.

"I'm lucky... If I'd passed away a year, or two years ago, I wouldn't have encountered (ChatGPT)," he said.

Suzuki said his old job exporting cars to Southeast Asia and other regions had helped him ask it the right questions.

"In my younger days, trading houses used telegrams to communicate -- you had to take care to send a clear message, in one short sentence."

The most popular of his apps is "Pee Count Record" which gets 30 downloads each week, despite no efforts being spent on marketing.

When Suzuki had hernia surgery two years ago, the nurses would ask him how many times he had passed urine.

But with the number as high as 12 a day after the operation, "I couldn't remember without recording it," he said, and so decided to make an app to help keep track.

The developer's older brother Kinji Suzuki, 92, uses several of the apps including "Voice Input Assist".

"It's handy because when you get old, it becomes bothersome to type," he said, demonstrating how to use the voice recognition tool to send emails.

- 'Good chemistry' with AI -

Etsunobu Onuki, 75, runs a hearing aid shop in suburban Tokyo where the younger Suzuki is a customer.

He uses a mouth-muscle strengthening app created by Suzuki called "A-I-U-Be Exercise" after the sounds the user is prompted to make.

"I always do it while sitting in the bath," said Onuki, who is also a fan of the new slideshow app, which stops him from leaving his house key in the shop when closing up.

"I want to recommend this app to my customers," many of whom are in their 70s and 80s and often forget to bring their registration card for the shop.

Suzuki is a member of a national group called the Senior Programming Network (SPN) and said other members have helped him along his journey.

SPN's founder Katsushiro Koizumi, 51, believes that "seniors and AI have a good chemistry".

He is urging members to go one step further and embed burgeoning generative AI tools within their apps, which elderly people can interact with.

"Users can operate the app by simply speaking natural language," because it is sometimes difficult for elderly people to hold down a button, or drag and drop an icon, on a small phone screen.

Suzuki agrees and said that although the hurdles are high to become an elderly app developer, "once you delve into this world, you will see that it's a lot of fun".

"If you don't have anything to do after retirement, please look into it. You could discover a new self."