Hello Tirthraj, please check out the following link for detailed info on NDA: https://competition.careers360.com/articles/nda-eligibility-criteria

You can definitely prepare for NDA at this stage, i can give you some preparation tips:

• be thorough with the syllabus
• make a study plan
• choose the right study material
• make short notes
• practice previous year's papers
• take rest and exercise, eat healthy and stay fit