Hey,

You can give the exam any number of times but you must be between 16.5–19.5 years on the date of Joining the academy. The eligible dates of birth will be written in the application form for the NDA exam. Also you must have passed class 12 at the time of joining. So the first possible attempt for anyone is when they are in class 12 in September(The course would start in the next year in July).