Is it permissible for a girl to marry a physically disabled young man despite her parents' objection?

You cannot marry this person except with your father's approval, as he is the guardian (wali) and marriage is not valid without him. Obedience to your father is obligatory in matters of common knowledge; this is because his desire for you to marry someone he deems suitable takes precedence over your own desire. Nevertheless, if the man is religious and of good character, you can try to convince your father to accept him by seeking the help of your brothers and paternal uncles.