DePetro was raised in Edgewood, Rhode Island, the youngest of seven children to Thomas and Virginia DePetro. With seven children in the house, the DePetro household was always bustling with a combination of comedy and debate. The DePetro children were encouraged to be competitive in both academics and athletics. At a young age DePetro was a competitive basketball and baseball player. Remembered by childhood friend Mayor Steve Laffey, "John DePetro was one of the fastest players I had seen in Edgewood sports. In baseball he could steal at will. In basketball he could race down the court making easy layups. I had never seen anyone so competitive at such a young age."