NDA

Yes, I can help you to prepare for your NDA examination. Here are some tips to begin.

Know the Syllabus and the Pattern of the Exam: Understand the syllabus as well as the pattern of examination to structure your preparation better.
Collect Relevant Study Materials: Use NCERT textbooks for core subjects; specialised NDA preparation books could be referred to in other subjects.
Create a Study Plan: Create a well-structured study plan which gives time to each subject, revision, and practice.
Core Subjects: Mathematics, Physics, Chemistry, and English have maximum weightage, so they should be the core focus.
Practice Daily: Attempt previous years' question papers and take mock tests to know your improvement in terms of time management.
Update Your Current Affairs: Read newspapers and magazines daily for better general awareness.
Physical Fitness: Do maintain physical fitness as it is essential to the selection process.

Age, education qualifications, and physical fitness criteria have to be looked upon to become eligible for NDA exam in 2024. If born in the year 2002, you are most likely eligible as age between 16.5 and 19.5 years allows for applying to the Indian NDA.

 For education qualification, you must have completed or must be appearing for Class 12 with Physics and Mathematics compulsory subjects. However, it is very important for the candidate to be physically fit, which would be evaluated in selection of candidates. One should also check with the latest NDA notifications published to know about any updates regarding eligibility and make sure that they meet them before applying.

Meeting the academics and age qualification is very important; however, physical and medically fit for selections have to be considered.

If you have already missed the deadline for the registration of NDA 1, you have to wait until the next round of applications. Usually, the round of application of NDA 2 comes a few months after NDA 1. The following are the steps to take:
Remain Updated: Continue to monitor the official UPSC website for release of NDA 2 application dates. NDA 2 application form usually starts in May.
One Time Registration (OTR): If not, do One Time Registration through OTR ID in UPSC portal, an all-India mandatory procedure. Prepare for NDA 2: The interim time can be used to prepare for upcoming NDA 2. Just refer to the relevant subject for your exam and practice last five years' question papers with detailed solutions.
Application Procedure: Once the NDA 2 application form is released, fill out the form, pay the fee, and submit all the documents.
Correction Window: If you have already applied but made mistakes, note that there will be a correction window after the application procedure closes, allowing you to make the necessary corrections.
Always check the official UPSC website for updates on application dates and procedures.

Since age limits prevent you from being eligible for the NDA, you have a few other options for pursuing a career in defence

After graduating, you can take the Combined Defence Services (CDS) exam, which grants you officer status in the Army, Navy and Air Force.
Technical Entry Scheme (TES): Based on Class 12 grades (for students in the Science stream), the Indian Army provides direct entry for those interested in technical professions.
After graduating, you can apply for a variety of officer positions in the Indian Air Force by taking the AFCAT (Air Force Common Admission Test).
SSC (Short Service Commission): After graduation take into consideration the SSC for officer positions in different branches of the military.

NDA preparation is a multidimensional approach imbibing academic knowledge with physical fitness and mental prepare. Here is a blueprint to get you started: 

Know the Exam Pattern and Syllabus: Well the NDA exam is divided into two papers:
Mathematics (300 marks)
General Ability Test (GAT) (600 marks), which includes:
English
General Knowledge (Physics, Chemistry, General Science, History, Geography, Current Affairs)
So, the first thing that you need to work upon is a clear and thorough understanding of the detailed syllabus for both these sections. You can refer to the official notifications by UPSC or trusted educational resources like Byju's or Gradeupudy Plan*:

Daily timetable with allocated time for every subject.
Revision and solving the previous years' question papers to get acquainted with question patterns and time management.
Focus on the weak areas, spend more time on preparation for such areas.
Mathematics Preparation:

Mathematics topics include Algebra, Trigonometry, calculus, and co-ordinate Geometry. These are very essential topics in terms of scoring marks.
Practice problem sets given in books like R.D. Sharma and M.L. Khanna.
Practicing continuously on online tests and solving problems of last year's papers build up the speed and helps gain accuracy really well .
General Ability Test (GAT):

English: Develop comprehension, vocabulary, and grammar. Grammar books by Wren & Martin and vocabulary books by Norman Lewis will help.
General Knowledge: Read newspapers, magazines, and online news sites. For static GK, read Lucent's GK or NCERT books on History, Geography, and General Science.
Physics and Chemistry: NCERT books for Classes 9 to 12 serve as a good base. For Physics also look at H.C. Verma.