No you cannot give CAT entrance examination right after your class 12th.
This is because,
To be eligible for CAT entrance examination one needs to be at least a graduate, as through CAT examination, admission in MBA is provided which is a postgraduate degree.
So, in order to be eligible for CAT ,after your class 12th you need to do graduation in any discipline.
For your reference ,
CAT eligibility criteria is provided below
To be eligible for CAT ,
you need a Bachelor's/graduation degree in any discipline from a recognised university .
you must have got at least 50 per cent marks or equivalent CGPA in your graduation . SC/ST/PH students need only at least 45 percentage in Bachelor’s Degree in any discipline to be eligible .
Candidates who are in the final year of their graduation are also eligible for CAT examination.
There is no age restriction to be eligible
It is not mandatory to have work experience to be eligible
For detailed information go through
Hope you are doing great as per the question asked by you, you can certainly give C.A.T entrance exam after completing your graduation or in the last year of your graduation but you can't give it after your class 12th exam.
The major M.B.A entrances that you can give are:
etc are some of the entrances.
Hope you found this answer useful.Stay motivated stay positive.
All the best!