Chaucer wrote the Pardoners tale between 1387-1400. During this time old men where a rarity due to poor choice of life and poor hygiene. People barely lived till their forties. Therefore Chaucer portrays the Old man as a wise and cultured individual "Though that I walked into Inde". Old men are the personification of wisdom and intellect, unfortunately when the three rioters refused to listen to the Mans advice it lead to their demise.
It can be argued that the Old man is a personification of Death. He could be in fact Deeth himself, purging the world from its filth. Especially these three rioters who have committed heinous sins.
The Old man can also be seen as a ironical tool used by Chaucer to depict the corrupt and hypocritical society of the time. The old man is tempered and calm, he does not take offense or insult from any of the rioters. The pardoner depicts an ideal 'christian' as well as christian morals through the Old man - "the hooly sacrament". Unlike the the rioters the Old man is sober and rational. Pardoner is aware of christian laws, yet he indulges in heavy drinking.
The Old man is supernatural, he is shrouded in a somber enigma soaked in mystery. It seems as though the old man was waiting specifically for these three men specifically to give warning about Deeth, Or it could be that he is an accomplice of Deeth and he wants to lure and entice them into their death. It is mentioned the old man is not allowed to die, this may give reference to the Bible and Jesus. There was a man whom blasphemed against God and therefore was punished to live a life of immortality to preach the word of God. He tells the rioters that even Deeth was not able to kill him.
The Pardoner uses to the Old man to scare his listeners to become afraid and purchase papal dispensations, to secure a place in heaven.
Chaucer uses the Old man to teach about certain truths, Respect of others. By behaving so loutishly to him, the three youths provide a reminder...