Heimdall: We know all of that. Pay attention to what she told you. Before she killed him he looked to be in his twenties. After the kill, the body rapidly aged and in minutes a 20 year old body turned into at least a 70 year old body.
This has nothing to do with dark side rot.
*Svafa nods in confirmation of what Heimdall had said*
"Dulce bellum inexpertis."
Official Forum Expert on Norse Mythology
As Odin says in the Hovamal:
"Praise no day 'til evening; no wife 'til on her pyre; no sword 'til tested;
no maid 'til bedded; no ice 'til crossed;
no ale 'til drunk."