Fimmel was born near Echuca, Victoria, Australia. He was raised on a 5,500-acre dairy farm in Lockington. The youngest of three brothers, he is the son of Jennie, a recreation officer for the disabled, and Chris, a cattle farmer. Aspiring to be a professional Australian rules footballer, Fimmel moved to Melbourne in his late teens to play for the St Kilda Football Club in the AFL, but a broken leg sidelined him before the season began. He was accepted into RMIT to study commercial architecture and engineering but later deferred to travel abroad.