Hey Abhishek
Yes you can give NDA exam after 12 th but with this subject you can go only in army wing.
And age limit is from 16.5 to 19.5
Height and weight and eye vision must be under the criteria limit.
Good luck

Dear Abhishek,

Yes, you are eligible to appear for the National Defence Academy Entrance Exam, although you will need to be within the age limit. The age limit for every candidate is 16&1/2 to 19&1/2 years old. By having the Science Stream in your 12th you can choose from the Army, Air Force, and the Navy, while those candidates that have taken Arts or Commerce stream in their 12th can only opt for admission under the Army.

Hope that cleared your questions, if not feel free to comment if you have any further questions.

Noo ....
You can't....