CAT is the entrance examination for admission to all the 20 IIMs. And there is no upper age limit for CAT. And the same applies to studying in IIMs as well. There is no upper age limit for studying in IIMs. IIMs shortlist candidates for the interview stage based on their own criteria, which may be independent of each other. The process may include Written Ability Test, Group Discussion, and Personal Interviews. Performance in the CAT examination is an important component in the admission process. IIMs may additionally use other factors such as the previous academic performance of the candidates, relevant work experience, gender and academic diversity and other similar inputs in shortlisting and ranking of candidates at various stages of the admission process. The processes, academic cut-offs and the weights allocated to the evaluation parameters may vary across IIMs. But few IIMs do not allow more than 8 years of work experience on an average. There are Candidates in their 35s who study in IIM. This iis because they put up Diversified Academic and work profiles and then join IIMs. So just to answer your question, there is no upper age limit for studying in IIMs.