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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
In principle it is permissible to wear the Qamees/Thawb (body-length garment), and a person will be rewarded if he wears it as a sign of following the example of the Prophet . Um Salamah said: "The best clothes for the Prophet was the Qamees." [Abu Daawood and At-Tirmithi] However, wearing the Qamees is not an obligation, while it is an obligation to obey the parents in what is permissible, and an obligation comes before what is desirable or permissible. Therefore, if one or both of your parents forbid you from wearing the Qamees, do not wear it as you are obliged to obey them, and you can wear decent and respectable clothes as many of them are available nowadays. However, if your parents order you to wear clothes that resemble non-Muslim clothes, or clothes that do not cover your 'Awrah (parts of the body that must be covered in Islam) and the like, then it is not permissible for you to obey them, as obeying Allaah and His Prophet comes before obeying the parents. Also, if they order you to shave your beard or to abandon praying with the congregation in the mosque, or order you to abandon other obligations then there is no obedience to them as the Prophet said: "There should be no obedience to a creature in disobeying the Creator." [Ahmad]
For more details about being kind and dutiful to parents please refer to Fataawa: 84942 and 86620.
Allaah Knows best.