{Thy Lord hath decreed that ye worship none but Him, and that ye be kind to parents. Whether one or both of them attain old age in thy life, say not to them a word of contempt, nor repel them, but address them in terms of honor}(Al-Isra, 17: 23).

So do not confuse the difference in opinion about who to marry with your duty to obey and respect your parents.

Second, put aside your own feelings about your girlfriend and think objectively about what your parents are saying, and in general the practicality of marrying a woman who is eight years your senior. You will be within Islamic guidelines of marriage if you marry her, but there are practical and personal considerations which must be taken into account. Give value to your parents’ opinions and realize that they have lived a long life and know much about human nature in general and especially about their own son. If you can arrange for your parents, especially your mother, to spend time with your girlfriend, that might help them to acquaint themselves better with who she really is as opposed to just being the object of a discussion about age the age difference.

Third, to be sure of what Allah’s plan is for you, be sure to perform the Istikhara prayer and seek the guidance and assistance of Allah as you come to a final decision about whether or not to marry this woman. If in your area there is someone available to provide premarital counseling, then you and your girlfriend should have several sessions of premarital counseling. Be open to the fact that you might discover things about each other or about each other’s views on particular issues in life, which will be quite different, and could lead to potential conflict later on in life. Do not disregard these issues, but do not also obsess about them. Strike a balance and be realistic in your final assessment.

Finally, there is no moment more special in one’s life than when one is guided by Allah to a sense of peace and tranquility about the decision to marry a particular person. If you are dating this woman, you might be deprived of such blessed moments from Allah. Therefore, while you are discussing marriage with her, please refrain from any premarital relations with her. You want to start your marital life free of sin. Repent to Allah, seek His forgiveness and be sure never to return to sin. Make du’aa for the best and Allah knows best.

For further guidance, please try the following link(s):
Getting Married!