system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The maximum limits to human lifespan appears to be around 120 years old. Why does the limit to human life expectancy seem to hit a ceiling at this particular point?
gpt
Imagine making a copy of a document with a scanner. Every time you scan a scanned document to make a copy it gets degraded. That's what's happening in your cells, a scanned copy of a scanned copy of a scanned copy. 

Now your body is doing that every few days or weeks depending on they type of cell. After 100+ years, it just gets degraded to the point where your organs start to fail. 

That's also how we get cancer, if you get a smudge on one of the photocopies and can't read it anymore, then keep photocopying it.