Minimum Age should be 16.5 years  and Maximum Age should be 19.5 years. Also, the date of birth will be calculated as it is entered in the Matriculation or Secondary School Leaving Certificate or in a certificate recognised by an Indian University as equivalent to Matriculation.

To check the complete eligibility, you cana go through the below link-

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

Good Luck!!!