You won't find any centenarians that eat vegan. India is one of the countries with the highest diabetes numbers and vegan. Japan, on the other hand, has the most centenarian and they eat basically unprocessed food and low carb.
Absolutely untrue. Adventists of the 7th day eat vegan afaik, and people in Okinawa ate very little meat. Both groups are famous for producing more centenarians than the average (global) population.
Correlation != causation. India is mostly vegetarian, not vegan - people eat diary products like paneer, ghee and yoghurt en masse. Meat foods are generally not that great - chicken with tons of bones, very chewy mutton, fish with tons of thin bones. I became +-vegetarian for few months when I backpacked there.
Their diet is generally not that good though - tons of carbs, little physical activity unless in 'blue collar' job. Older folks are almost always overweight. Maybe genes also don't help, not sure there.
Blue zones are the 7 areas of the world that disproportionally produce centenarians.
Studies of their diets indicate that almost all of them are primarily vegetarian and they receive the majority of their calories from carbs. Feel free to look into them. Note that the blue zone in Sardenia is a big outlier even within the group.
https://www.seventhdayadventistdiet.com/