All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The scholars stated that it is an obligation on a son to obey his parents if they order him not to marry a specific woman as a way of giving priority to their desire and will over his own will, provided the parents have a sound religious reason for refusing, or a reason that is usually accepted according to custom.
If this girl is religious and has good moral conduct, then you should try to convince them to accept your marriage to her, however, if they insist on refusing, then in principle you should obey them as we clarified.
However, if you fear committing prohibitions with her or with other women, then it is permissible for you to marry her even if your parents disagree.
Nonetheless, we advise you to stop thinking about her and look for other women as there are many pious women out there. Usually, the view of the parents is more correct in such situations. The marriage that is preceded by such matters does not usually lead to a stable marital life.
You should continue to be kind and dutiful to your parents and be keen on pleasing them in any case.
It should be mentioned that the difference of age or the fact that your sisters are not married are not at all impediments to marriage.
Moreover, you should not have told your parents that you plan to commit what Allaah has forbidden. If you feel you must tell them, then you may say instead something like, ‘I want to protect myself from prohibitions’ and other similar expressions.
Finally, it should be noted that you are not permitted to commit what Allaah has forbidden, and your parents refusing your marriage to this woman is not an excuse with Allaah.
For more benefit on the ruling of marrying without the consent of parents, please refer to Fatwas 92340, 89650 and 83379.
Allaah Knows best.