In the excerpt from "The Fish" by Elizabeth Bishop, some words or phrases tha compare the fish to an old experienced soldier are:
Like medals with ribbons frayed and wavering: the fish got away and survived, and now as an experienced soldier waves his medals with ribbons.
beard of wisdom trailing from aching jaw: an old soldier that was injured, moving slowly on the ground.
victory: this is the goal of a soldier after the fight. In this case was the fish that was finally caught "filling up the little boat."