Hello student I'm sorry to inform you but candidates need to be in between of 16.5 years to 19.5 Year to appear in NDA exam as per the eligibility.

Qualification eligibility - candidates must passed or appearing class 12 with physics chemistry and mathematics with minimum 60 percent marks from a recognized board.

For more updates refer to the link mentioned below

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

Feel free to comment if you have any doubt

Good luck