Aaron grew up in Ramsgate but began his career at Gillingham FC as an apprentice. In October 2013, Millbank joined Ramsgate and impressed during his spell with his hometown club, scoring eight goals in 26 appearances.
In February 2014, Millbank was recalled by Gillingham for inclusion in the first team squad. Aaron made his professional debut for Gillingham in May 2014, replacing Cody McDonald in a 1–1 draw with Shrewsbury Town.
Aaron missed 2014/15 and 2015/16 due to injury, however, he re-signed for Ramsgate in the summer of 2016.
Aaron Millbank is sponsored by Amcol Engineering for the 2016/17 season.