It is not possible for a student to enroll himself without having institution. You can approach the commanding officer of the nearest NCC unit for taking guidance. You can apply for senior division as your age is 22. The maximum age a student can apply for National cadet Corps service is 26. After completion of training the NCC unit provides you B and C category certificate because of not having NCC in your college. After approaching to the commanding officer, the commanding officer will verify it. After verifying your medical examination will be done.

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