In IITM i can only get Naval Architecture and Ocean Engineering. I thin\k i want to pursue mechanical engineering but i cant say for sure. I was wondering if I could take Ocean engineering and then pursue Aerospace Engineering in my higher studies if I participated in relevant projects and took relevant courses.
You can read this article. It will give you some insight on the parameters you should consider while choosing your branch.
It depends on the requirements of the Aerospace Engineering graduate programs you are interested in. However, most graduate programs are very competitive, so keep that in mind.
Hope that helps!