system
Given the following post, respond as if you're commenting on Reddit:
human
What causes my dog to age and die much faster than my kid?
gpt
There is no concrete answer to why different animals have dissimilar life spans. One theory is that the life span is dictated by how long creatures need to stay alive in order to ensure the survival of their spieces. Some animals can procreate within two months and die within 2 years (mice) so as not to overcrowd their environment. Others, like humans take ~12 years to reach puberty, take care of our young for ~17 years on average, and need to stay alive to defend and provide for the race. We don't have any natural predators, so we don't need to multiply like rabbits to ensure our survival. This is the strategy evolution has funneled us into.   

Another theory is that each animal has a certain metabolic rate that relates to their life span. Basically, some animals live fast and die young while others live slowly and die old.