Am I obligated to marry a girl whom I promised to marry nine years ago, and who has refused all suitors waiting for me, or should I obey my parents who refuse my marriage to her because of the age difference?

Fulfilling a promise is enjoined by religious law and praised naturally. It is a characteristic of prophets and righteous people, while breaking a promise is a characteristic of hypocrites. If fulfilling a promise conflicts with obeying and honoring one's parents, then honoring parents takes precedence, because it is an obligation, whereas fulfilling a promise is considered merely recommended by some scholars. Therefore, we advise you to obey your parents and try to satisfy them, and if you cannot reconcile the two, then honoring parents takes precedence.