system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Aging: how does it work? How does the body/cells one day know to start deterioration instead of growth? Why, when I'm young, can I regenerate tissues faster than I could in 30 years?

Basically just need an explanation as to how aging works, and why it works.
gpt
Have you ever tried using a copy machine in an office or library to make a copy of a copy? The words come out kind of blurry even though the one you put in the machine can be read clearly. 

That’s kind of how cells work. Your body is pumping out copies and gets it really close each time, but over years the cells just get a little worse at their jobs since they lose a few words from their instruction manual each time they copy.