Dear Student,
It's good to hear that you want to do CA, you can appear for CA foundation just after your 12th being from science background is no problem. Students from every streams are allowed to appear for CA but being from a completely different stream it'll be a bit difficult for you to do CA but you can cope up by doing some coaching for it which would be helpful and definitely it's not a big problem if intended you can easily deal with it. Hope this might help you.