CBSE 12th

It is not an issue. You must have done 12th from a recognised board and graduation from a recognised university.

CAT does not have any upper or lower age limit. However, the eligibility criteria for CAT states that the candidate should have completed their undergraduate degree with a minimum of 50% for the General and NC-OBC categories (45% for reserved categories).

Some companies may require 60 % but it is okay to have 50% as many companies accept student above 50% .You can overcome this with value addition courses.

The eligibility criteria of NATA 2023 is given below.

Eligibility: Candidate should have passed an 10+2 examination with at least 50 percent aggregate marks in Physics, Chemistry, and Mathematics. 

So, 50% in PCM is mandatory requirement, so you can't give NATA exam.

Yes, you can do 12th in other subjects also but not as regular student. You need to go for NIOS on demand exams in desired papers. Visit NIOS on demand exam website for more details.

You can join Indian Army through NDA after 12th. Whereas in Police, many post like constable, Havaldar etc. can also be joined after 12th. However higher qualifications are the best. Top UPSC exams like CDS, AFCAT, Civil services etc. can be attempted after the graduation. So B.Sc. PCM can be the best options after 12th.

Yes. CG PET syllabus is similar to the 12th standard syllabus. The subjects, unit and topics to be studied for CG PET is similar to the ones that are prepared while tempting the 12th standard board qualifying examination. Therefore, the candidates will be able to prepare simultaneously for CG PET and their 12th standard board exams. However, there might be minor changes in the syllabus so the candidates are advise to check the official CG PET syllabus prepared by the authorities. The CG PT syllabus will be available online at the official website. 

Yes, you can get, but write about the college name for better response. Private universities like LPU can give you the admission in B.Teach CSE. But you need to appear in LPUNEST scholarship exam. The eligibility criteria is given below. 10+2 with minimum 60% aggregate marks with Physics, Maths and English.

Admission criteria: JEE Main, LPUNEST or CUET