Hi, A bachelor's degree in finance or business administration is required to become a stock broker. On-the-job training programs or internships are often available to aspiring stock brokers, which allow them to gain practical experience and work towards earning the needed professional licenses.
So after 12th in your under graduate course you can study BBA/BMS and further get experience in the same.
Stock Brokers is an old term and now basically they are called as financial analysts.

Hope this helps.
Good luck.