Taxonomy. The average size for an adult female American alligator is 8.2 feet (2.6 m), and the average size for a male is 11.2 feet (3.4 m). Exceptionally large males can reach a weight of nearly half a ton or 1,000 pounds.merican alligators may live to about 50 years in the wild. After it is four feet long, an alligator is safe from predators except humans and occasionally other alligators. All or part of this information was provided by the Animal Diversity Web and Museum of Zoology of the University of Michigan.