To apply for IIT JAM examination, you must satisfy the IIT JAM Eligibility Criteria: -

you must have a bachelorís degree with at least 55% marks if you are from General or OBC category and 50% marks if you are from SC/ ST/ PwD categories.

You must have science as a subject in you 10+2 level.
Both Indian & Foreign candidates are eligible.
There is no age limit for IIT-JAM exam.
Students appearing for their final year exams are also eligible.