CBSE 12th

You should go for B.Com as it has many good options as compared to BBA.

Doctor (MBBS)
Academician (B.Sc)
Physiotherapist (BPT)
Occupational Therapist (BOT)
Biotechnology and Genetic engineering
BAMS
BHMS
BBA
BMS/BCA (if you have maths)
Law
BJMC (mass communication)

India's top aeronautical engineering or aerospace engineering courses are at IITs, IIST and PEC University, Chandigarh. Admission in these universities is based on JEE Mains and Advanced scores.
Some private universities such as Manipal University and Amity University are good for aerospace engineering. These universities conduct their own engineering entrance examination.

I am not sure about that but you can ask the same by contacting the admission cell.
Help Desk Telephone no.: 0172-2753813, 2753814 Contact Info: (From Monday to Friday, 9.00 A.M - 5.00 P.M)

It will depend on your preparation if your preparation is good for JEE and you are sure to qualify then you can. Preparing for past two years will not be deemed worthy if you didn't follow the right path.

Hello Dheeru,
There are different types of eligibility criteria. One talks about the year in which you have passed your 12th. In your case, it's ok. Other criteria is the date of birth. Now, for this, visit the website and you will come to know if you are eligible or not.

You can do it before your results. You will be called for the admission test and personal interview. If you are selected you will be given a provisional admission. After your results are out you will need to upload your results.

Good chances of getting a call for GD-PI round.

You can join IFS by appearing for civil services examination conducted by UPSC on completion of graduation degree from a recognised university.