If it’s about diet, then what’s so special? African countries have simple and natural diet too, why doesn’t that work?

Quality of life in Japan vs an African country isn’t comparable. It’s a combination of a healthier diet and higher standard of living. Also, it isn’t unlikely that some of those people’s ages aren’t accurate.

Generally to grow old: be content! You don’t need heaps of money, don’t fill a hole in yourself, that’s unfillable, live reasonable (!) healthy, do things in reasonable doses, learn your whole life and in particular: don’t try to get old. It’s not the length of the way, it’s what you experience during your journey.