Scientists discovered the famous mouse to elephant curve, which measures how much energy an animal uses when at rest. It shows that the smaller a warm-blooded animal, the more energy it needs to burn per ounce of body weight even when it is doing nothing. The reason for that curve is that the smaller an object the larger its surface area to volume ratio is. That means a mouse has a lot more surface area per cubic inch of body than an elephant. Since heat loss to the environment is proportional to surface area, small animals lose body heat to the environment a lot more quickly than large animals. Warm-blooded animals like birds and mammals must eat to replace the lost body heat, unless they go into hibernation.
Eating is not enough, because the food needs to be converted to heat and oxygen is also required. To supply the body with the needed oxygen, the heart of a small animal has to beat more often. A mouse for example has a heart rate of 500 beats per minute. Since the heart beats non-stop even before birth, it can only last so many beats before it fails. Cats and mice and in fact most mammals have hearts that last a similar number of beats. Cats have a heart rate of about 133 beats per minute, or about 1/4 of that of a mouse. A mouse lives a maximum of around 3 years before its heart fails. A cat can live 4 times as long before its heart will fail.
We humans have a heart rate that is less than 1/2 that of a cat so we should live twice as long as a cat. Instead, for some reason, primates evolved to have hearts that are 3 times as strong as mouse and cats, so we actually live 6 times as long as cats do before our hearts fail. Elephants have even lower heart rates than us humans, but unfortunately for them their heart is not as strong as ours, so they only live to about 60 years old. Besides their teeth wear out after about 60 years and they starve to death anyway.
Cold-blooded animals like frogs, lizards, snakes and turtles do not burn energy to replace lost body heat so they can live a lot longer than similar sized mammals, since their hearts do not have to work as hard. Whales also live longer than us humans because they are big, and they are well insulated by blubber, so they don't burn much energy and their heart rate is also low enough for them to live over 100 years. The longest lived animal is an arctic clam, which lives to about 400 years old, because it uses little energy due to the cold temperatures in the Arctic. That means the key to a long life is to use as little energy as possible. Indeed scientific experiments have shown that not only worms live longer if they are underfed, but even humans will live longer if we are slightly underfed.