Most of your body is younger than you are. The cells on the topmost layer of your skin are around two weeks old, and soon to die. Your oldest red blood cells are around four months old. Your liver’s cells will live for around 10 to 17 months old before being replaced. All across your organs, cells are being produced and destroyed. They have an expiry date.

In your brain, it’s a different story. New neurons are made in just two parts of the brain—the hippocampus, involved in memory and navigation, and the olfactory bulb, involved in smell (and even then only until 18 months of age). Aside from that, your neurons are as old as you are and