Describe symbolism in The Life and Opinions of Tristram Shandy by Laurence Sterne

In Volume Seven, Tristam implies that Eugenuis' earlier depiction as Yorick's faithful adviser is merely a symbol of Tristram's own relationship with Eugenuis. In fact, as far as the Yorick story is concerned, Eugenuis should be far older than Tristram, yet Tristram presents Eugenuis as someone near his own age.