Linking the agricultural cycle of planting, growing, harvest with the human lifecycle is a very common metaphor.

We see this in the myth of persephone, where going into the underworld and returning (ie death and rebirth) is a metaphor for the harvest cycle. Greek mystery cults were all over this too and it's likely a pre-greek remnant from the Early European Farmers who inhabited the area before steppe-descended greek speakers began moving in.

So the association of death and harvesting probably starts fairly early.