HELLO,Student 

Well , i thought you are talking about NDA exam , so any 12'th appearing student can fill the NDA form , you age must be 16.5 to 19.5 years.

so, you are eligible for NDA as per you class and i don't know your age. visit the below link to see in details about nda and it's eligibility criteria

https://competition.careers360.com/articles/nda-eligibility-criteria

all the best!!