People say someone died of old age, but no death certificate says that. What they are describing is real all the same: a very old body slowing down across every system at once, until it stops. It usually looks like less eating, more sleeping, and a steady pulling inward over weeks to months. Here is what it actually looks like, and how it differs from dying of a named disease.
The signs below overlap with dying from any cause, covered in what dying actually looks like. This page is about the specific, slow version that comes with great age.