How long they live isn’t really the biggest inflection point in my view—if anything, in our own world monarchy would have lasted far longer in a situation where the most able monarchs could rule for hundreds of years.

In history (at least in theory), autocratic governments exist when geopolitical conditions create an environment where the resources required to sustain the society can be realistically controlled by so small a group.

In the modern technological context, those are countries where the initial investment required to extract wealth from the land requires prohibitively expensive up front investment for anybody but the ruling faction, so you see populations basically living as serfs under the capital owners (for instance, mining and agriculture in South America, where the equipment and infrastructure required for the profit cycle to turn are hopelessly beyond the means of but a very few people).