Hello Amakmaraniket,

               For IAS exam conducted by UPSC first of all you should be at least of 21 years of age.

          Secondly you should hold a graduate degree from any recognised university under any stream or course. 

            Also you should be a citizen of India. 

  For appearing in IAS exam you need not to worry about your 12th  as all you need is just pass marks in all the subjects to get a seat in any college or university from where you can pursue your graduation or higher studies.

 Basically you must be a graduate to appear for IAS exam

GOOD LUCK