Guys bore hora hu, CA krlu?

Actually I am in 12th and want to pursue career in mba (from IIM Blackism ofc).
But I cannot give CAT before my bachelors.
Should I start prep for CA just after 12th to get some knowledge/workex.
Thinking of getting into dummy articleship, is it good or bad decision.
I heared that inter course is similar to whole b.com, is that true?