The only thing that makes sense of this counsel— to follow your own desires, knowing that God will bring you to account for them at the last Day— is to have right desires. And the only way to have right desires is to desire what God approves. And the only way to desire what God approves is to be given new desires. And the only way to have new desires is through the new birth.
How gracious of God that the young may rejoice and be cheerful in good ways that will stand before His judgment.