O'Neil was born in Boulder, Colorado and attended Dennison Elementary.His family hired him an acting coach after he did well in school oralinterpretation classes. O'Neil subsequently won five silver and onebronze medals at amateur acting competitions during the summer of 2005and was taken on by Cutler Management, who sent him to study acting.Shortly after that, he was cast in The Last Mimzy (2007), which was hissecond acting audition.O'Neil lives with his family in the foothills outside of Denver, Colorado,near the Rocky Flats Plant. His favorite video game is The Lord of theRings: The Battle for Middle-Earth II (2006) (VG). As of March 2007, he isin sixth grade and attends school on set while filming. He has an olderbrother, Tyler, and comes from a "very Christian" family.