No, unfortunately, ISI Kolkata does not provide undergraduate courses on computer science. However, the proposal for starting B.Tech in computer science has been put forward but has not landed to any conclusion yet, and is being said that in the coming future this proposal may be accepted. 

For now, the present scenario of the undergraduate course in ISI Kolkata would just be B.Stat and B.Math. They both contain extensive teaching in computer programming as well as statistics. 

B.Math is a combination of computer science and pure mathematics and statistics. Whereas B.Stat contains lesser topics of computer science in their syllabus than B.Math.

Taking a course at IIT is just as difficult and demanding as pursuing a B.Stat course at ISI. They are whatever you choose to do with your life, whether you like mathematics/statistics enough to spend three years learning statistics (and a little math) and statistics solely at ISI, or you believe you are skilled in another subject that has a good course at one of the numerous IITs.

It depends totally on where you want to be. Furthermore, even if you prepare for college X, there is no guarantee that you will be accepted. As a result, keeping colleges Y and Z in mind as a backup is always a good idea.

Only you can decide which option is preferable for you and what you want. 

Both B.Stat and B.Math are different courses being offered at different campuses at ISI Kolkata and ISI Bangalore respectively. There are only a few common subjects in both courses. 

The choice ultimately depends on your choice and interest. You can go through the syllabus of both courses and understand the topics. Find whichever interests you, you can choose to be research-oriented like B.math students or go for M.stat or other courses, if you choose so.

You can apply for only 1 course because the institute conducts the entrance of both courses at the same time and day. You will be able to appear for only one of them.

There are three sections in the entrance exam and the level of maths is the same as what you studied in your 12th. The exam follows the pattern of most high school mathematics competitions (RMO, INMO, etc).

The three sections of the Entrance Exam consist of MCQ, A Subjective Test, and an Interview.

The books you must know are:

1. Problem Solving Strategies by Engel Arthur
2. Test of Mathematics at the 10 + 2 level, Indian Statistical Institute, Published by Affiliated East-West Press Pvt. Ltd.
3. Challenge and Thrill of Pre-College Mathematics by B. J. Venkatachala

You should complete these all and do previous year’s papers of ISI/CMI RMO, INMO and IMO.

For Interview:

• Once you crack the exam, the interview part won’t be that difficult.
• Answer the questions confidently and honestly.
• The entrance exam of ISI is not easy and also there are only a few seats for B.Stat. 
• You have to prepare well.

Do not overthink and do your preparation well. This will help you a lot. Be calm and try to think of cracking the exam and the latter part would be an easy task for you.

First of all, please do not worry about the age limit because as a 20-year old you'll definitely be considered for entrance exams. There is a rule which states that you cannot appear more than the fixed number of times for the same exam, but there's no rule which bars you because of your age. 

You'll find that you will have seniors in your batch too and maybe those with similar concerns, such as yours.

As for the admission process, you do not have to worry about looks, age, number of years, height, weight, or skin color. Except for your appearance and behavior, the rest is overlooked. Also, you must be fast at calculation and logic to do well in the interview. 

One of my friends graduated from ISI, Delhi Campus. So I might be able to give you some information about it.

• For the Kolkata and Delhi campuses, I don’t believe there are separate MSQE exams. 
• When filling out the application, you must choose between Kolkata and Delhi.
• If nothing has changed since 2009, which I assume it has, you will only have to take one exam and select your campus on the application form.

However, in Delhi and Kolkata, interviews are performed at the relevant locations. That is, students who are chosen in a Delhi interview are admitted to ISI Delhi, and vice versa.

ISI Kolkata is considered to be a good institute for B.Stats. It accepts admission purely on the basis of the entrance exam and the interview. The minimum eligibility criteria for the entrance is 70% in class 12th boards. 

The selection process will be finalized upon your performance in the entrance exam and the interview session. With this score, you will be able to pass through the cutoff but you must have an exemplary performance during the interview session.

All the courses of ISI Kolkata i.e. M. Math, M. Tech (CSE), M. Stat, MSQE, and M. Tech QROR have the same placement rate that is 100%. All the courses have a placement rate of 100% and every student of ISI Kolkata either gets placed. 

The only thing that differs in all these courses in terms of placement is the time when they get placement. The students from one course get placed earlier than the other. M.Stat students get placed earlier than the MSQE or M.Tech students. According to the average package, the students of M.Stat usually receive a higher average package. However, MSQE or M.Tech students also get higher packages in some years. The average CTC offered at the institute is 19 LPA.