If my date of birth is 15 jan 2003 ,so how many times we attempt for nda written exam

You need to be between 16.5 and 19.5 years to appear for NDA exam. Which means if you are appearing for NDA 2020, you need to be born between July 2nd 2001 and July 1st, 2004. For NDA II, you should be born between 2nd January 2002 and 1st January 2005. As of today, you are 17 years and 2 months old. You can appear for NDA until 2022. Considering the fact that NDA exam is held twice a year, you have 4-5 more chances approximately.