As you want to get the details of will you be able to submit the application form of NDA after class 12th so here is the information of the same for you:

I want to tell you that you are not eligible for the exam of NDA

You will become eligible after passing class 12th

Here for your reference I am giving you the eligibility criteria of NDA exam:

Nationality:
A candidate must be either be a
(i) a citizen of India , or
(ii). a subject of Bhutan, or
(iii). a subject of Nepal, or
(iv). a Tibetan refugee who came ovbet ot India before the 01 January , 1962 with the intention of spermanently settling in India, or
(v). a Person of Indian origin who has migrated from Pakisthan, Burma, Sri Lanka and East African countires of Kenya, Uganda, the United Republic of Tanzania, Zambia, Malawim Zaire and Ethiopia or Vietnam with the intention of permanently setting in India.

Age:
Candidates must be in between the age of 16.5 years to 19 years

Educational Qualifications:
(i)For Army wing of National Defence Academy:
Candidates must have passed class 12th or equivalent examination conducted by a State Education Board or a University.

(ii) For Air Force and Naval Wings of National Defence Academy and for the 10+2 Cadet Entry Scheme at the Indian Naval Academy:
Candidates must have passed class 12th or equivalent with Physics and Mathematics conducted by a State Education Board or a University.

Contact Details:
Union Public Service Commission
UPSC,
Man Singh Road Area,
New Delhi,
Delhi 110069
India

Map Location: