Mahatma Gandhi University, Bangalore

Yes, you can join any college/university for B.Sc in maths. Age doesn't matter. You can apply for private and government colleges.

The minimum eligibility criterion needed to be met for pursuing B.Sc in mathematics is a 10+2 or equivalent qualification in science or commerce stream with a minimum score of 50% in mathematics from a recognized educational board.

What is your preferred location?

You can directly apply to the college and thereafter you will be called for the final admission. You need to have passed graduation from a recognized university.

Please refer to the link provided below for details regarding fee structures of M.sc. courses in Mahatma Gandhi University, Bangalore. You can download their brochure which should yield accurate results regarding fee structures for the course mentioned above.
https://www.shiksha.com/college/mahatma-gandhi-university-bangalore-35307