Joining International Baccalaureate (IB) course can be at any time. The IB preparation is altogether different from other professional courses like IIT. All the teachers employed in such coaching classes are not being that experienced. On the other hand, the IB school teachers are handpicked and are with high experience and educational background.   

The number of students in IB classes is also less, say 20 percent of those IIT coaching institutes. Hence personal attention is assured and in turn better score in the examinations.

If the financial backing is sufficient, you can get into IB coaching even before the 11th grade.

IB education is not cheap at all. The total expense towards coaching, books, miscellaneous expenses, examination fees, and travel, accommodation etc. would be on the higher side for middle-class families. But that is cheaper than IIT coaching and is comparable to usual school fees nowadays. 

In  other words, if the financial situation allows you there is no harm in joining for IB classes anytime before the 11 th grade.
With an IB diploma in hand getting admission in both foreign universities and most of the Indian Universities would be a cakewalk.

If the student starts early in IB coaching, they get better breathing time and hence they would be better prepared for the final examination. They get better base in the core subjects namely Language and Literature, Language Acquisition, Individuals and Societies, Science, Math, and the Arts.

Only those students who have attended IB coaching at school or institutes are eligible to take up the IB examination.