As for whether they can live so long because they eat green food all the year round, I don't think so. Green food is also natural food. Except now, people used natural food in the past, and all of them were green food. We don't see how many people live long. Most of those who live long are just rumors and have not been confirmed. Most of them are mysterious and have nothing to do with green food. They may live a long life for various reasons, but I don't think it includes green food.
Moreover, the length of life and how long you live are two different things. You should never judge the length of your life by how long you live. Most of the ancients died young because of natural and man-made disasters. From here, we can't draw the conclusion that the ancient people lived longer or shorter than us. But according to rumors, people who live long are people with high spiritual cultivation, and most of them are people who practice Buddhism and Taoism.
Therefore, it is also the secret of longevity to relieve depression from time to time, maintain peace of mind and exercise hard. Because now science has long proved that the emotional fluctuation of distance is harmful to the body every time. Whether it is happy or sad, a peaceful mind is the secret of longevity.