You should be between 16.5 years and 19.5 years to appear for NDA Exam. Now if you were born on September 25th, 2002, you are 17 years and 8 months old. And NDA exam is held twice a year, in April and September. So you can appear for NDA until September 2021 because by April 2022 you are already 19 years and 6 months old. For more information, please read our article: https://competition.careers360.com/articles/nda-eligibility-criteria