Hello aspirant!  Let me inform you that yes it is mandatory to pass in class 12 examinations if you are planning for JEE MAINS OR JEE ADVANCE. This always remains first criteria. You can appear for jee advance for two times and three times for jee mains. It is not mandatory to be a fresher to give these examinations you can be a dropper as well. You must not be more than 24 Years of age. There is relaxation of 5 years for SC, st, pwd, candidates.