[4] Kooij rode for the Forte U19 Cycling Team and Willebrord Wil Vooruit as a junior, before signing for the Jumbo–Visma Development Team for their inaugural season in 2020.

He finished second to David Dekker,[5] in his first UCI race with the team at the Ster van Zwolle, before he took three successive victories – either side of the enforced break from racing due to the COVID-19 pandemic – at the Trofej Umag, the Poreč Trophy and the GP Kranj.

[6][7][8] He competed at the Czech Cycling Tour for Team Jumbo–Visma, with Jumbo–Visma Development Team colleagues Lars Boven, Owen Geleijn and Michel Hessmann.

[10] The following month, he won the opening stage of the Settimana Internazionale di Coppi e Bartali in a sprint finish, ahead of Ethan Hayter and Phil Bauhaus.

This biographical article related to Dutch cycling is a stub.