It is rather a crucial decision which you have finally taken but in this process, there is always the possibility of loosing two years in the wake of changing your stream from commerce to science. If you have taken your admission in class eleven again with the science stream so to complete 10+2 board with science, it would take two years tenure for its completion with your changed stream.
Taking up your admission in the open schools such as IGNOU, Karnataka Open University, Manipal School of Distance Education etc is not practically possible due to attachment of practical components of your theory papers of Physics and Chemistry.
Hope that with your changed science stream, you have passed your 10+2 successfully and are appearing for JEE main, it could not create any hurdle in your mission except loosing two academic years.
Even in respect of age, no minimum or maximum age has been prescribed, you can sail through JEE main provided you qualify the cut off points.
Now talking to your chance for appearing JEE advanced, you need to ensure that your age has not exceeded beyond twenty five years on the previous year ( as on 1st October ) if appearing for the next year. Of course age relaxation to the extent of five year is applicable depending your cast status.
You can appear for JEE advanced maximum for two years subject to fulfilment of your age criteria in your case.
Hope you would consider these points prior to taking up your final decision.
