Flanders was born in Hastings and attended Hastings [Boys' High School] where he played rugby for the first XV, originally as a halfback before converting to loose forward. His performances for the school earned him selection for the New Zealand Schools side in 2021. After leaving school he joined up with the Hurricanes academy, representing their U18 side in 2021, and U20 side in 2022. In 2023, he was selected for the New Zealand national under-20 [rugby union team|New Zealand U20] side. He is the brother of fellow and player Devan Flanders.