Olayinka began his career with Arsenal.[3] He signed his first professional contract with the club in January 2019.[4]
On 29 August 2020, Olayinka was named an unused substitute in the 2020 FA Community Shield, with Arsenal clinching a 5–4 victory over Liverpool in the penalty shootout after the match finished 1–1 after 90 minutes.[5]
Loan to Northampton Town
In January 2020, Olayinka moved on loan to League Two side Northampton Town until the end of the season,[6][7] making his debut in a 3–0 win over Scunthorpe United on 28 January.[8] He helped Northampton Town to secure promotion to League One by winning the play-off final.[9]
Loan to Southend United
In October 2020 he joined Southend United on loan until January 2021.[10] He scored his first goal for the club, and his first professional goal, in an FA Cup tie against Boreham Wood on 7 November 2020.[11] On 1 February 2021, Olayinka extended his loan with Southend United to the end of the 2020–21 season.[12]
Cheltenham Town
He signed a two-year contract with Cheltenham Town on 1 September 2022.[13] On 2 January 2024, manager Darrell Clarke announced that Olayinka had been made available for transfer.[14]
He was released by the club at the end of the 2023–24 season.[15]