system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If the cells in our body keep renew constantly the why people are getting old?

ELI5: Aren't if the loop keep going on then we suppose to be young forever as long as the body getting nutrients and energy?
gpt
To renew themselves, they copy themselves. Each time they make a new copy it’s just a little less perfect than the last one. An analogy would be making a photocopy of a photocopy of a photocopy until it’s no longer a readable image.