NDA age limits is between minimum 16.5 years to maximum 19.5 years during during the commencement of course. And you must know that NDA is conducted twice a year so a person who falls in this age group get two chances for NDA in a particular year.

Now as you said your date of birth is 21 February 2006, and you are going to pass 12th in 2024,  so that time your age will be somewhere around 18 years.  But according to rule of NDA, Candidates who are appearing in the 12th Class under the 10+2 pattern of School Education or equivalent examination can also apply for this examination.  So in before passing 12th, in 2023 you will get one option for NDA.

So your total chances are as follow :-

In 2023= 1 attempts

In 2024= 2 attempts

In 2025= 1 attempts as you will be crossing age limits most probably if exam dates even goes up slightly.

So your total number of attempts will be atleast 4.

It was a good question. Thank you.