Any caloric restriction extends life purely by virtue of limiting IGF-1. Scientists have made mice live as much as 50% longer than normal by using severe caloric restriction. It has nothing to do with plant based food, it's correlation that vegan diets tend to be nutrient deficient leading to low IGF-1, but you could achieve the same results using fast food if calories and protein are controlled. The flipside is that this leads to lower quality of life. Weaker bones, less strength, weaker immune system. Life extension is largely a trade off. This is why vegans are overwhelmingly slim, weak, frail, and sick more often, no different to anorexics.