India

You have lots of options to appear for this examination,lets see the options for this examination.
N.D.A examination.
C.D.S examination.
SSC(Technical)
NCC Special Entry
You are not eligible to appear for N.D.A examination because to appear for this examination.The applicant's age should have a minimum 16.5 years and maximum 19 years at the time of appearing and the applicants must have passed the intermediate examination from a recognised School.This examination is conducted twice in a year by Union Public Service Commission.So,I think you are already crossed 19 years so you are not eligible to apply for this examination.
Procedure to apply for C.D.S examination :-
C.D.S I.e Combined Defence Service Examination is conducted twice in a year by UPSC(Union Public Service Commission) for recruitment of O.T.A/I.M.A/Air force/Naval Academy course.To join this course,the candidate has a minimum qualification is a graduate degree from a recognised University and those in the final year of degree course can also apply for this examination.
Important dates for this examination(C.D.S I) :-
Date of Notification :- 29/10/11
Last date for receipt of application :- 28/11/11(already closed)
Date of examination :- 12/02/12
If you have not filled the application form, so you missed this chance to appear for this examination but worry next notification will be published in the month of June or July in the official website or employment news paper.So,regularly Visit the official website of UPSC.
Let see the eligibility criteria's for this examination and the eligibility criteria vary from post to post.
I.M.A(Military Academy) :-
Minimum qualification for this examination is a graduate degree in any desire subject from a recognised University or equivalent qualification and applicant's who are completed or appearing in the graduate degree can also apply for this examination.The applicant's age should have a minimum 19 years and maximum 24 years and unmarried male candidates are eligible to apply for this examination.There is no minimum marks for this examination and No arrears at the time of appearing for this examination.