Hii Rohit,

Hope you're doing great.

Union Public Service Commission (UPSC) will release the eligibility criteria of NDA 2021.

Candidates should be between 16.5 and 19.5 years to apply and minimum education required for NDA is 10+2 for army and 10+2 with Physics and Maths for Air Force and Navy.

You can check out this link below for additional information-

https://competition.careers360.com/articles/nda-eligibility-criteria

For study, NCERT books of 11th,12th and some other questions solutions are well enough for this exam.

Hope this helps you!!