Born in Colorado Springs, Colorado, Carlo was introduced to hockey at age 5 when he started playing roller hockey with his neighbors and quickly fell in love with it. He grew up idolizing Hockey Hall of Fame defenseman Rob Blake after he saw him play for the Colorado Avalanche while attending his first NHL game.
Carlo won a silver medal at age 16 playing with the United States at the 2013 Ivan Hlinka Memorial Cup and twice competed in the IIHF World Junior Championship, winning bronze in 2016. He was selected by the Boston Bruins in the second round (No. 27) of the 2015 NHL Draft and signed a three-year, entry-level contract on Sept. 25 of that year.