It is obligatory for a woman to cover her face before non-mahram men, according to the more correct of the two scholarly opinions, because of a great deal of evidence which we have quoted in the answer to question no. 11774.
It is not permissible for a girl to obey her father or mother by not covering the face if she is convinced that it is obligatory, because there is no obedience to any living being if it involves disobedience towards the Creator.
And it is not permissible for the father to order his daughter to uncover her face, even if he thinks that niqaab is mustahabb, because she is enjoined to do what she knows and is convinced of, and she will be questioned about that, not about the convictions of her father or his opinion. If she does not wear niqaab then she is disobeying her Lord, so what benefit will she have from obeying her father in that case?
The Prophet (peace and blessings of Allaah be upon him) said: “There is no obedience if it involves disobedience towards Allaah; obedience is only in that which is right and proper.” Narrated by (al-Bukhaari (7257) and Muslim (1840).
You should strive to advise your parents and convince them that you are entitled to freedom in choosing the opinion which you think is correct, whether it is on the basis of knowing the evidence or by following a scholar whom you trust, and according to sharee’ah it is not permissible for you to ignore this opinion just because it goes against the opinion of your father or mother. Not covering the face means that you are falling into sin and disobedience, whether you do it once or twice or more. Every time you appear before non-mahrams with your face uncovered, you are sinning thereby.
Perhaps it seems to you from this answer that the issue is not about convincing your parents that niqaab is obligatory, because you may or may not succeed, depending on whether you present the evidence clearly or nor and whether you are able to convince them or not. But the issue that you should focus on is the idea that a girl should follow her father’s opinion, and it is not permissible for her to give up something that she is convinced of because of his opinion, and it is not permissible for him to force her to follow his opinion.
This is an issue concerning which there is a difference of scholarly opinion, and the difference concerning it is to be respected. In such cases we must be gentle when speaking to parents about it, and be patient in dealing with them, and not think of them as sinning and disobeying Allaah, or turning away from His laws. Perhaps they are convinced that it is not obligatory, just as you are convinced that it is obligatory, and because it is their duty to care for you and bring you up, they may think that preventing you from doing something that is not obligatory is their right.
It seems from your question that your parents are not opposed to the principle of covering the face, but they think that you are too young for it. This is something that it will be easy to convince them about, because if covering the face is obligatory, then the girl who has reached adolescence is required to do it, and she is sinning by going against it, and it makes no difference whether she is 14 years old or 20.
As for the problems that are expected if you insist on following your opinion and going against your parents, these are regular problems which will ease with the passage of time and as your parents get used to seeing the niqaab. It needs patience and sacrifice, and it is sufficient for the believing woman if her Lord is pleased with her, even if people are not pleased.
Some fathers are afraid that if their daughters start to wear niqaab at a young age, they may be put off after that and will take it off. Hence we say: Show how convinced you are of the niqaab and how keen you are to wear it and adhere to it, and try to dispel their fears. And some of them are afraid that if she puts on niqaab, no one will see her properly and that may affect her chances of marriage later on.
To sum up: what we advise with regard to this problem is to be patient in dealing with your parents and seek the intervention of someone who can convince them, if possible. Bring them some tapes of scholars who speak of that, and tell them again about what has convinced you that it is obligatory, so long as you are sure that the source is trusted by your parents. But if you think it most likely that the problems with your family caused by your wearing niqaab will be more than you can bear, then perhaps you can delay it for a little while until they are convinced, or until their objections have died down, but you should avoid going out of the house or mixing with non-mahram men as much as possible. If you can put it on in the street, where they cannot see you, that is also good, in sha Allaah.