Since Homer wrote primarily from a male perspective, we can roughly equate a generation with the average age of marriage for males in Ancient Greece, which would be around 30 years. From the female perspective, it would be 15 years. For the wife to be fully accepted into the groom’s family, a child had to be conceived from their union as soon as possible after marriage.
The only exception would be Sparta, where men married around 20 years of age, but would spend most of their time in the barracks until they reached the age of 30.