Son wants to try for NDA after class 12, and we have nobody in the forces to ask

He brought it up again at dinner last week, this time with details: the written exam, the interview that runs over several days, the physical standards. It started with a talk at school by a retired officer, and unlike most of his plans it has lasted more than a month. Neither my partner nor I have anyone in the forces to ask, so I am trying to separate what I have read online from what is required. A few specific questions: 1. Does he need maths in class 11 and 12, or only for some wings? 2. Do most applicants join a coaching programme, and if so, from which class? 3. Is there anything sensible for a 14 year old to do now, apart from staying fit and keeping his marks steady? Experience from families whose children applied would help most, whether or not they got in. I don't want to discourage him. I would like him to go in knowing what it involves.