i’m worried my brother is becoming a alcoholic

i’m posting here because i’m worried and i don’t know what to do. he’s 21 and i have many stories of his drinking but ill talk about the highlights. he’s driven a car drunk atleast once to my knowledge, and has driven both a jet ski and a boat drunk multiple times. he frequently blacks out when he does drinks and sometimes goes on binges up to 14-15hours long with his friends. but sometimes he is capable of only having a few like 3 or 4 and calling it a night depending who he is with. he spent so much money probably 1500 a month on just alcohol and going out. he probably drank 3-5 days a week when he was moved out but he just moved home. i don’t know if this is just a phase and he will grow out of it now that he’s living with my parents again. i don’t think he’s physically dependent on because he can go some time without it. i do not know if im over reacting