How can one respond to those who say that the niqab is not obligatory, or that "I am still too young to wear it," or who inquire about the reason for my wearing the niqab?

Religious rulings are tied to puberty. Once a boy reaches puberty, he is no longer exempt from accountability. As soon as a discerning girl reaches puberty, she becomes like other accountable women, and she must observe the regulations of the legal hijab. The jurists have agreed on the obligation of covering the 'awrah (intimate parts) for both adult men and women. Scholars have differed regarding the obligation for a woman to cover her face, and the preponderant opinion, which is the one we issue fatwas according to, is that it is obligatory.