Symbols - What does heaven look like
Geras was the personification in the Greek system of the system or function of ageing.
Given that our cells are constantly being replaced, there is in theory no reason why we should age or even die, thus the Greeks recognised that there must be a process at work - a function that determined that at a specific point we started to age in a process that would terminate in death.
Geras was depicted as a tiny shrivelled up old man. His Roman equivalent was Senectus. From the name we get such terms as geriatric.