If I recall my hair didn’t stop changing until I was into adolescence (I’m white) and my brother had blond hair until he was 5 - now it’s dark brown.
By 3yrs old my lots hair didnt change anymore
My boys hair started changing at 7 months and it’s still changing now at 9 months x
Thank you for your responses everyone x
honestly it’s different for everyone but i’d say well into childhood