Hi Pratyush,
Since you are determined to become a doctor right at this early age, the first thing you should remember is be focused on your goal.
Make sure your concepts are clear. Whatever you study in your course curriculum, should be conceptually clear to you without any mugging up.
If you have interest in Biology, its a very good thing. If you don't, start taking interest in it and you will love the subject.
Some students join coaching centers right from class 6 or 8. Even if you don't, its perfectly alright. Just be focused and study hard and sincerely. You may consider taking admission in coaching after you pass your boards.
If you have any other query, feel free to comment below.
Good luck to you!