Hey there
No ofcourse not 21 is a standard age to start preparing for sbi po you are very young and can crack sbi po if you prepare in a right direction. CA is a course and SBI PO is an aptitude test and in CA you can have many attempts but in sbi po there is age limit. If you want to prepare for sbi po then go for the best course on careers360
Check the link
https://www.google.com/url?sa=t&source=web&rct=j&url=https://learn.careers360.com/knockout-sbi-po/&ved=2ahUKEwiXtYz64qjqAhUHWCsKHdzZAvIQFjABegQICRAB&usg=AOvVaw2RtlUtbudWQFaIA0lBw30n
Good luck
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