There is no upper age limit for admission to higher secondary courses in any State. You can get admission to any of the Boards you have mentioned. In West Bengal, the admission process starts after the publication of the results of Madhyamik examination in June every year. You have to apply to individual colleges. Admission for Maharashtra Board HSC courses begin after the publication of the SSC results in the month of May. You can apply to any college under the Maharashtra Board subject to the minimum aggregate marks (in the SSC or equivalent examination, which in your case is the Madhyamik examination of the West Bengal Board of Secondary Examination) asked by the college. For example, for students coming from States out of Maharashtra, St. Xaviers College asks for at least 80% marks in aggregate for admission to Science stream. Besides that, you have to submit a Certificate of Eligibility from the Mumbai Divisional Board of the Maharashtra State Board of Secondary and Higher Secondary Examination. This is meant to certify that the Madhyamik examination is equivalent to SSC examination of the Maharashtra State Board of Secondary and Higher Secondary Examination.