My age is 31 year and should I go for MBA?
Why I am not recommending you full time MBA because most of the companies prefer freshers or the students with 1-2 years experience in their company. I am currently studying in 2nd year at IIM Kozhikode and I have seen my batchmates who were having more than 3+ years work experience struggling to get an internship during my first year. They might also face problem in final placements which hasn't been started in my college for my batch. Also in my junior batch one of the student was same like you who was aged joined full MBA programme and unfortunately he signed out from internship placements as he wasn't getting any company's shortlist.
Whereas for my college only executive MBA program runs at another campus in Kochi. Placements there are pretty good and you will have a very good chance of ending up with a good job.
So I highly recommend you to do executive MBA program from a premier institute rather than doing full time MBA program.
All the best!!

Regarding fees you can easily get loans at a very cheap rate if you are in a premier b-schools. They even offer loans without any guarantee because of the trust that a student from a premier b-school will end up with a good job.
If you can get admiration in FMS or JBIMS then your money problem will also be solved. FMS is one of the b-school with best ROI. I don't know about executive MBA program but in 2 year full course it's fees is only 20000 for 2 years and average package is around 20 Lakh per annum. In JBIMS Mumbai also fees is very less.