Career
Allen began his career at Fulham, where he spent a year in the youth team before being released due to his size. He also had a trial with Reading, and then joined Barnet in the summer of 2011, signing a two-year scholarship. In January 2013, Allen signed a "long term" professional contract with the Bees.
He joined Kingstonian on loan on 10 January 2014.
Then, on 19 February, he joined Redhill on loan. Allen scored his first goal for Barnet in a 3-3 draw at Lincoln City on the final day of the 2013-2014 season.
He joined Wingate & Finchley on a three-month loan on 23 October 2014. On 28 July 2015, Allen following his release from Barnet signed for League Two side Yeovil Town on a one-year deal.
On 1 February 2016, Allen signed for Torquay United from Yeovil until the end of the season.