Born in Somerville, Massachusetts, Hepburn's family moved to Los Angeles, California when he was ten years old.

He began riding motorcycles as a teen and his skills led to him signing on with a cycle performing group in 1914 that toured the West Coast and parts of the American Midwest.

[2] He began winning consistently thereafter and in 1921 won the "Dodge City 300 National Championship" while breaking all existing 300 mi (480 km) records.

That year, he rode to his second victory in the 300 mi (480 km) National Championship motorcycle race, this time at Meridian Speedway in Wichita, Kansas.

Hepburn then lent the motorcycle to Indian rider Joe Petrali, who won the race and shared the prize money with him.