Dear student,

As per the basic eligibility criteria of NDA ,  any student whose age lies between 16.5-19.5 years, is eligible to give this test. And also, you must be either in 12th class or you have passed 12th class. Now currently your age is 16.5 years. But we don't know about your current class. But you fullfill the age criteria. So, it is hard to comment about no. of attempts. You can go through the link given below to check the eligibility criteria of NDA exam.

https://www.google.com/amp/s/competition.careers360.com/articles/nda-eligibility-criteria/amp

Hope it helps.