Our bodies undergo wear-and-tear, like the mailbox we had to fix last week. Only, in the case of our bodies, we don't yet have a way to fix or replace most of our parts. After a while, too many parts get worn down until they are no longer able to continue, and everything about us - the parts that allow us to think, the parts that allow us to feel - just stops.
Sadly, fixing our biology is harder than fixing mailboxes, and while we're learning more and more about how to do it every decade, we won't be able to fix everything for the foreseeable future.
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Too accurately:
So why aren't we trying harder to fix it? You see, son, society has been dealing with death for many thousands of years, and people have developed coping mechanisms to deal with its apparent inevitability. The majority of people simply don't think about it. Public figures have even rationalized death as a good thing, and boy have they said the darndest things. For example, I've recently read of someone comparing our bodies to legos in a fixed sandbox - as if people literally need to be disassembled before others can be born - and no one bats an eye! Another person pointed out that scientific progress would be slowed down without the older generation of scientists dying - sure, billions of non-scientists may die every few decades, but hey, science is a bit faster as a result!
The point is, society has created a culture of either ignoring or accepting death, and it shapes the very way we think. Sure, that culture might have been harmless back when we really had no chance of combating problems like old age, but now? The vast majority of researchers, of funders, don't even bother to think about what should be some of the most important problems of our generation. Until we have progressed to the point where it becomes blatantly obvious that the technology to combat old age exists, it is unlikely anyone will even notice it. In other words, we're all screwed and you were born a few hundred years too early.