Hello,

CA will be difficult as compared for SBI PO. you can try for CA. you can appear again for coming year with better preparation. for CA or SBI Po, there is no attempt limit or age limit. you can appear for multiple times.

it is okay if your have no knowledge. You can start from now. if you study hard and schedule your time then you can manage to cover all the topics and prepare well.

try solving  example questions multiple times. solve excersices. attempt mock tests. solve previous year question papers. Give your best.

Hope it helps!