Hello dear
You can't joinMBA Coursejust after 12th board , forMBA Courseyou should have to appear for graduation course and after that you can appear for MBA Course as well Exam . For MBA Course you should fulfill certain eligibility criteria forMBA Course.
So , here is the eligibility criteria for joiningMBA Course
You should haveBachelor's Degreeof at least 3 years for MBA Course .
You must have at least50% marksfor being eligible .
Candidate appeared for final year exam are also eligible for admission.
No age limit forMBA Course.
Inorder to get masters you need to have bachelor's degree too

after 12th is not possible,

There are two aspects for doing MBA
1. Full time MBA programme

Eligibility require to do MBA:-
A candidate must have any Bachelor degree with minimum 50% marks from any recognized university if you belongs any reserve category you need only 45% marks in your bachelor from any recognize university and Institute.

A Final year students and Result awaited candidate may also apply for the course.


2. Part time MBA Programme: A candidate just need to passing percentage in his/her bachelor degree for Part time programme.

I suggest you get admissted in any bachelor degree programme first and when you are in Final FinAL YEAR start preparing MBA Entrance exam like

CAT
MAt
XAt
SNAP etc

and after your exam of final; year just take MBA entrance test to get admission in any good MBA College.

All the best!