Hey there

If you want to become a doctor you have to do mbbs for that. For mbbs neet is the exam you may give to get admissions into top colleges of India. MBBS in India is 5.5 years then you may go for md also. Neet has no age limit but biology is necessary as your subject for neet.

Check detailed eligibility for neet

https://www.google.com/url?sa=t&source=web&rct=j&url=https://medicine.careers360.com/articles/neet-eligibility-criteria/amp&ved=2ahUKEwjk2uKe5KPlAhVi7HMBHYq9CkoQFjAAegQIAhAE&usg=AOvVaw3J48XLYjRlxkl5RSraYMod&ampcf=1

Good luck