How do you interpret the simile describing the old man's scars in the old man and the sea: "They were as old as erosions in a fishless desert."

The operative word here is "old". Santiago's scars are old, "The blotches ran well down the sides of his face and his hands had the deep creased scars from handling heavy fish on the cords. But none of these scars were fresh...." Santiago is old and he has not caught anything close to the grandeur when he was a younger man. Santiago's life, once so filled with the bountiful water filled with fish, has dried up. The simile gives us a sense of how Santiago's meaning for life, his dreams, have dried up with age.