Different parts of the body have different biological clocks, with varying cell turnover rates.

“different parts of the body have different clocks of course we all know that different organisms have different lifespans dragon flies have 24 hours cuttlefish live one year tops mice a few years we wouldn't dare even ask what it would mean for a human to live a good life if life was only 24 hours long but our bodies are not just one thing we have dragon flies within us we have cuddlefish within what I mean is that we have some cells that turn over extremely rapidly like endothelial cells and some that never do like neurons we're not just one thing we're not just one age”