Her parents refuse to let her wear niqaab because she is young
Question

                I am a 14-year-old girl. Studying in the second year in secondary school. I wear hejab that covers my entire body. My clothes are very baggy and I cover my neck and chest by my khimar. Nothing appears of my body apart from my face and hands, as explained by many scholars that face and hands are not ‘awra. There is disagreement amongst scholars regarding hejab, yet I try my best to cover more of my body. I have tried so many times to convince my parents to allow me to wear niqab, but they refuse saying that I am still very young and that I just reached the age of puberty two years ago. What shall I do? Shall I obey them and they will bear the sin before Allah, or shall I disobey them and insist on wearing niqab in order to be closer to Allah? If I insist on wearing it, this will cause many problems to me and they will be displeased with me. What shall I do?.
Praise be to Allah.Firstly: 
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. 
Secondly: 
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). 
Thirdly: 
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.