Simon Hughes was hunting with his dad on their 5,000-acre ranch, when they had an encounter with the 800-pound reptile.
The Telegraph quoted Simon as saying: "I wasn't afraid for a second. Next year I'm going to kill me a bigger alligator."
He added, "My friends were proud of me and I was proud of myself. It's humungous."
Simon, who trained to shoot guns a year ago, is also adept in driving all-terrain vehicles.
His mother Toni Hughes said, "It sort of scares you to death because there are alligators, there are snakes, all sorts of things out there.
"What we thought was massive was a 10 foot alligator, and this one just dwarfs the 10 foot. It's just so massive and prehistoric looking."
Simon's trophy - the alligator's head will be mounted and bookshelves will also be made out of it.