What is it about certain animals that makes them live longer?

In a nutshell, the longevity of an animal, all else being equal, has a good deal to do with whether it is burning the candle at both ends or not. The longest living animals are some arctic clams. Because of the cold temperatures in the arctic, the metabolic rates of these clams must by necessity be low. Growth rate is slow as a result, and life span gets stretched, over that of clams that live in warmer waters. You may have heard that slight starvation lengthens the lives of animals from worms to rats. Starvation forces the body's metabolic rates to slow down, lengthening life span because there is less wear and tear of the body's vital organs, and the cells' vital parts.

Reptiles and amphibians are ectotherms, meaning they do not generate internal body heat to maintain a high body temperature. Their heart rates are therefore correspondingly slower because they do not have to supply as much oxygen to all the cells in their body as much as an endotherm, such as a mammal or bird, does. As a result, a frog or a lizard may live longer than a cat or a dog because they are not burning the candle at both ends constantly just to stay warm. Further, small endotherms, such as shrews and mice, have even higher metabolic rates than large endotherms, such as elephants, because their body surface to volume ratio is higher. Since heat loss is proportional to surface area, small endotherms lose heat to their environment much more easily and must replace the lost heat to stay alive. As a result, a small endotherm such as a mouse may have hearts that beat as much as 500 times per minute. In contrast, humans have heart rates that are only about 70 beats per minute because we are much large than mice, and our body surface area to volume ratio is much lower. Needless to say, having a heart that beats 500 times per minute is equivalent to burning the candle at both ends compared to an animal with a heart rate of, say, 50. The life expectancy of mice is therefore only 2-3 years. Dogs are better than mice, since they are larger, and their heart rate much lower, about 100 beats per minute. However, there is yet another factor besides metabolic rate that determines life span, and that is genetics. Genetics and differences in heart rate are responsible for our longer life span than dogs.

For some reason, some animals simply live longer because of genetics. For example, birds tend to live longer than mammals of a similar size. The hummingbird, for example, may live 3-4 times as long as a mouse, even though it has a similar heart rate as a mouse. Primates, too, live 3-4 times as long as the average mammal of the same size. As a result, we live 3 times as long as a donkey or a horse, even though we are actually smaller than donkeys and horses. We live 6-7 times as long as a dog because we have a heart rate that is about half that of a dog and we live 3-4 times as long as a mammal with similar heart rate as we do. To sum up, life span varies because of genetics, metabolic rate, body size and whether an animal is "warm" or "cold" blooded.

Every different variable can increase or decrease an animals life expectancy. For example, what the animal's habitat is like, diet, natural selection (Survival of the fittest), domesticated or wild, etc. Living in the wild is hard.