Is it haram for 13 year old boy to look at breasts?

Yes, it is haram to look at breasts, this is forbidden to see and you should keep your gaze away from it as much as possible. To prove it's haram, if you ever watched pornography you should notice that your heart feels like a rock and you feel nothing. It's an addiction that never stops and not only that but physically damages your body if you masturbate also. Please do not look at these haram things they will make you addicted and will lead you astray, may allah help you, if anything I said wrong may allah forgive me, and anything I said correct may allah guide you to the right path, insha'allah.