Hi Jagdeep,

NTA publishes revised eligibility criteria for the JEE Mains and JEE Advanced every year. There is no particular age-limit for JEE Mains. Any student who has passed 12th or its equivalent exam in the year 2020, 2021 or is due to appear in 2022 can apply for the entrance exam. Hence you need not repeat your 12th.

Coming to the subject criteria, for getting into a B.E./B.Tech course, a student should have passed the qualifying exam with Physics, Mathematics compulsorily with any one of Chemistry, Biology or Biotechnology as Technical/ Optional/ Vocational Subject. For getting admission in B.Arch he/she should have passed the qualifying exam with Physics, Chemistry and Mathematics.

The eligibility for JEE Advanced isn't dependent on your board marks. It solely is dependent upon your performance in JEE Mains. Every year a cutoff marks is set by the organizing IIT for qualification in JEE Advanced, depending on overall performance of all students. If you clear that cutoff, you will be eligible for Advanced.

It is advised that you check NTA's brochure for JEE Mains and Advanced eligibility when they are published. You can refer here for latest detailed information on JEE as announced by NTA:

https://engineering.careers360.com/articles/jee-main-2022

Hope that helped. Best of luck!