Hello,

To be an astronaut there are some requirement to be fullfilled and it will take a long time. It is same as someone doing PHD. Getting a wide recognition will take your most valuable time.

here are the requirements:-

• a Bachelors degree in engineering, biological science,physical science,mathematics or computer science.
• 3 years of experience after completion of your degree or worked for 1000 hours as a pilot in command time in jetcraft
• Ability to pass NASA test which is a time taking physical test. Your distant and near acuity must be correctable which means if it is  not then it can be made to 20/20 for each eye. Use of specs or glasses are allowed.

These are the requirements. You can get more details from the NASA website.

LInk:- https://www.nasa.gov/audience/forstudents/postsecondary/features/F_Astronaut_Requirements.html

So for you after 12th you have to do Bachelors degree in any of the above mentioned domain.

Hope it helps!