As per the eligibility criteria, the candidates must have passed 10+2 with Mathematics and Physics and any of the subjects among Chemistry or Biology or Biotechnology or Computer Science or Computer Application as compulsory subjects from a recognized board. The candidate must has passed all the subjects individually in both theory and practical examination. An aggregate of at least 45% marks in the three compulsory subjects are required for general category candidates to be eligible for WBJEE and also have passed English with at least 30% marks. There is no upper age limit in WBJEE except Marine Engineering. The candidate applying for WBJEE must be at least 17 years old as on December 31 of the year of examination. Now you have passed 12th three years ago. So you must have completed 17 years age. So you are eligible to appear for WBJEE 2021 if you meet other eligibility criteria as well. Check it here
http://engineering.careers360.com/articles/wbjee-eligibility-criteria