When can I start building muscles really?

well im 15 and i really started wen im 13 im pretty big....i eat right i ussualyy have some egss and oatmeal have some kind of protein for every meal i also take protein shakes and it is all legal. and i have a hard srious work out 4 days a week for almost an hour so u can start wenever but u jus gotta eat right