system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what causes death from old age?

Why is it humans rarely make it to 100 let alone 100+ what is it that gives out to cause death assuming no illness and why is it so rare for humans to live to that sort of age but some animals have been known to live way over 100.

Edit: ok so I get that basically our bodies stop bring able to repair themselves/keep parts working but why is it that some animals can do it for far longer?
gpt
You don't actually die from old age. Most people die from Pneumonia or some other complication that has to do with aging.

Bust basically your bodies cells are constantly dying. Your entire bone structure is replaced every 10 years. Your skin gets replaced roughly monthly.

As you age you replace dead cells less and less effectively. Until you cannot replace cells effectively in a key place and you die.