Government & Defence Entrance Exam

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.

If you have filled the Jan form, you can expect the admit card by the month of June.

Hi Abhishek,
Firstly, you need to have a graduation degree along with it and you should start early the preparation for UPSC and thoroughly search out what all subjects preparation go with the exam. All the information you can get from the official website of UPSC and after that, be regular with your preparation as this exam demands a lot of time and dedication.
Good luck.

JB, As per the past few years of trends the Delhi is the best for UPSC (IAS/IPS) coaching. The following IAS Coaching Instituts can be the best for preparation.
1. Vijiram and Ravi IAS Coaching Institute
2. Plutus IAS Coaching
3. Analog IAS Academy
4. ALS Academy
5. Drishti IAS Coaching