Born in Fort Collins, Mill moved with his family to Laramie, Wyoming, before relocating to Aspen, Colorado, in the early 1960s. Mill was an accomplished junior racer and made the U.S. Ski Team in 1971, and in 1974, Mill competed at the World Championships in St. Moritz, Switzerland. For the next seven years, when not injured, he was America's top downhill racer. In the mid-1970s, Mill was nicknamed "Wilde Hund" (wild dog) by Europeans for his gritty style and appearance (long hair & beard).