What is the remedy for repelling the devil's whispers to commit fornication and his saying, "Do it then repent," for a young man who has not yet married and has reached the age of thirty?

You must increase your supplication and fervent prayer to Allah to turn your heart away from disobedience, and keep away from environments that encourage evil. You should also seek out righteous companions who will help you do good, listen to beneficial lectures and admonitions, and hasten to take the steps towards marriage while seeking Allah's help.