Mac began skiing before he reached the age of two years at Bromley Mountain in Vermont. Both his parents, Libby and David, as well as his older siblings, Lexi and Cody, were avid skiers. Originally from Madison, Connecticut, at age thirteen Mac moved to Lake Placid, New York, in 2008 to pursue his dream of becoming an Olympic skier. Two years later he moved across the country to Park City, Utah. He attended middle school in Connecticut and then did high school classes through an online program. His parents remained in Madison, so Mac moved to the Olympic Training Center by himself.