 Mills also played for Long Buckby's youth team, and was part of the team that won a national under-16 competition.He started his senior career at Forest under the management of Brian Clough, making his first-team debut in a 2–1 victory at home to Arsenal in the First Division on 9 September 1978, and in doing so became Forest's youngest league player at the age of 16 years and 203 days.Mills signed a professional contract with Forest on 13 November 1978, two days after his 17th birthday, after serving his apprenticeship He scored his first goal for Forest with the opening goal of a 2–1 win away to Leeds United on 15 May 1979.