Actually instead of going for full time MBA you should go for executive MBA. Executive MBA is especially made for guys like you who want to do MBA after a good experience. Many a times company itself send it's employee to do executive MBA and take burden of all the expenses. But in your case the situation is different becuase you are a school teacher so you would need to bear expenses by yourself.

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!!