hey

well if you want to become a police officer you have to be of 21 years and you need to write a competitive exam like ssc constable,civil services exam and other recruitment examinations,well after you complete your 10th and you can take any subject like arts ,commerce or science  for your 10+2 and after that you and you have prepare for the examination as there will be alot of competition and many peopledo attempt them.

for more detailed info: https://school.careers360.com/articles/career-as-police-officer