Hello Sameer,
For joining IIT it is required for a candidate to be 12th passed with a good percentage and this will not be enough.
For getting into IIT the candidate has to clear the competitive exams JEE MAIN first and if the candidate qualifies in Jee main then he has to qualify JEE ADVANCE. These exams are very tough and there is a huge competition in this exam.
Almost every year around 11lac students appear in JEE mains exams and only around 2lac students qualify for the next level.
After the student qualifies jee advance and if he has a good score or good rank then only he will get a seat into IIT.
There are 11,289 seats in IITs in India and 11 lakh people apply for this so the competition is tough.

So you can join iit only after 12th exam.
If you want to join iit coaching it will be better to join it as soon as possible.
Hope this may help you.
All the best.

No, you need to qualify JEE MAINS & Advanced to  get admission in IITs, and JEE is based on Ur 12th syllabus. So u can't join IIT from 10th STD, u need to complete Ur 12th board with minimum of 75%.
    Now ,if u are asking about joining any coaching institutes for IIT preparation. Then yah, u can join those institutions after 10th. Or even after 12th ,if u take a drop year.
   Hope u got all ur doubts cleared. Feel free to ask more if u have others too.