Business Management Studies

It is simple.
Step 1 - Know if you like numbers and lot of calculation and formula if number of Finance is out of your bucket.
Step 2 - Are you interested in earning money? You can't sit at one place you need to or like to interact with professionals every day, you are ready for a rigorous work, choose Marketing.
Step 3 - Do you like a stagnant life, fixed income interact with new people fresher etc. go with HR.
In simple words, when marketing is compared with Finance and HR, there is more growth in your life, but be ready for some field work ( not selling door to door ).
I assume you already know the difference between Marketing and Sales.
Marketing will fetch you more money and experience as a fresher, by the end of BBA you will be able to decide what will be your cup of tea in MBA. For me personally HR and Finance sounds very executive but at some time these things will get boring, choose wisely.

Hi Kirti,
Yes, it is absolutely possible to get admission for MBA not at the age of just 26, but even at the age of 36. No problems in getting admission, but problem may arise in placements which you need to smartly tackle. Certain point to say in this regard:
#1): You need to have valid reason to explain your year gap since you aren't have any work experience. This 'un-reasonable gap' may restrict you to get admission in top B-Schools.
#2) Same thing you have to do during placement as top- companies choose the student with academic consistency. However, what you can explain to them is that within these years, you have acquired certain skill-set which stands you apart. Additionally, you have to prove (by your entrance marks) that you still have good grasp on your intelligence. Be honest and explain everything very smartly and straightforward.

I would say UPES without a doubt is better in placements for MBA students, especially if you are a mechanical graduate. It has 96% placements in last 3 years, and is consistently ranked amongst the best universities for MBA placements. Furthermore, UPES also has consistency in MBA placements and fortune 500 companies regularly recruit MBA students from UPES. Not only this, UPES has many specialised MBA programs that you can pursue which are not available in other universities. These MBA specializations have immense scope and the placement record is also top-tier. The overall package offered to MBA students in UPES is also higher. A lot of fortune 500 brands that specialize in mechanical engineering recruit MBA students from UPES. Brands like Volvo, Eicher, Maersk, Adani, and others hire students from UPES. So, I will suggest you go pursue MBA in UPES if you want a good placement. Also, it is in Dehradun, which is nice place to study and the weather is also really good.