Hi Bablu,
Everyone has their own capacity many students start preparation in class 9 and many starts in class 11 and according to my personal experience I have seen both of them crack JEE advance so don't think much and start doing whenever you want no matter which class you are studying right now.In many places foundation class start from class 7.Even if you realise on class 12 you can also crack depend upon your labour and strategy.
Thank you.
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