Your decision to choose a specialization in engineering or any other discipline should be based on the demand and supply in the job market, if your goal is to get employed in that particular field soon after you graduate.
If there is no demand in the job market for your specialization, you will find it hard to get a job in your field. Why spend so much money and time on college to learn something you are not going use at a job and later forget everything you studied ?
Demand for aerospace engineers is very low especially in the private sector, not just in India but across the world. If your goal is to get a job as an aerospace engineer immediately after the degree, this is not a good idea.
However, if you want pursue master’s and PhD in aerospace engineering and make a career as an academic and/or get a research position in private or government organizations you can study aerospace engineering for B.tech. Remember, this is a very tough road, you should be quite confident that this is what you want to do in your life. Your chances of success will be affected negatively due to lack of (private and government) funding in this area.