Here's something I didn't know

In biology, some animals have what's called negligible senescence:

[N]egligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly senescent animals do not increase with age as they do in senescent organisms.

In other words, they tend to live until something actively kills them. They're still vulnerable to disease or violence, but absent that they just keep living. Examples include some tortoises and -- get this -- lobsters, who can live 100 years.