[4] Once again finishing as top scorer in the youth set-up, he turned down a trial with Chelsea in order to join AFC Wimbledon.
[3] Kaja signed a professional contract with AFC Wimbledon in April 2015, and made his first team debut on Saturday 26 September.
[11] In July 2018, Kaja joined newly promoted Scottish Premiership side Livingston on a season-long loan but was recalled by new Wimbledon manager Wally Downes in December.
[16] Kaja received his first international call up at the Albania national under-21 football team by coach Alban Bushi for a gathering between 14 and 17 May 2017 with most of the players selected from Albanian championships.
[12] Upon signing for Livingston on loan, player-manager Kenny Miller described him as "quick, powerful and direct" adding that he "will bring a different dimension to our offensive options".