Government & Defence Entrance Exam

Yes, you can. It's your last chance. The age must be in 16 plus to 19 plus.

For army wing, you should have passed or appearing in +2 exam and for naval and air force wing +2 with maths and physics. Age should be in between 16.5 to 19.5 years. All the best.

For joining as officer, you need to go through NDA exam, and afterwards if you are graduate, then there is also direct recruitment exam held by air force. All you need to prepare for exam, physical and interview. All the best.

Hi Rimjhim,
You can go with any field as you can become IAS officer after any field but if you are firmative with that you want to become IAS officer then you should go with Arts field as many subjects are related. But if your interest is in other field after studying that also you can go for IAS officer.
Good luck.

At his current age of 18, he is eligible to apply for the exam.

Almost all government jobs are open to people of all educational background. They only specify the min. Educational qualification.

Army recruitment drives often takes place across the country. They usually release advertisement regarding these recruitment drives. Look out for them.

It is great that you wish to join the Indian Army. There are many job roles hence sharing with you the link please read the same:
https://www.shiksha.com/humanities-social-sciences/articles/career-in-army-blogId-923.