Am I Eligible For NDA 1 2023 ? National Defence academy which is the Only Tri Services Academy which  trains Army,Navy and Air Force Cadets Together. Age to Reach NDA is 16.5 to 19.5 yrs To reach to National Defence Academy one has to go through 3 Stages: Stage 1- Written Exam Stage 2- SSB Interview Stage 3- Medicals and Final Merit To Cross these 3 Stages one takes 11 Months thus Age For Form Filling of NDA Exam is 15.5 to 18.5 yrs.Keeping this age in mind for NDA 1 2023 Imp dates are as follows:- Form Opens- 21