I did MBA in marketing and have no interest in the marketing field & am interested in chemistry field, I am 28 years old, what can I do?

You can still do a job, and side by side do any course in Chemistry of your own choice. This will help you justify your interest and will keep your MBA degree worthy enough till you get a job in chemistry/pharmacy or any such field. Moreover, this will justify your age as well to an interviewer. We