Help in forced marriage

i am student of engineering age 19, my girlfriend is just about to turn major in 1 month... c belongs to higher caste, hence her parents dont accept me... they are planning for her marriage as soon as c turns 18... they'll get marriage registered and then she will study her higher education... after her graduation they will marry her traditionally... what legally we can do? if she refuse to register marriage then they will torture her and certainly her studies will be canceled... and on other i cannot elope with her due to my age... is there any legal way that c may do as they say for now (get registered), till they let her study her graduation.. and elope after 4 years... if yes then what need to b done??? my family is ready... but wants to complete study first... any suggestion???