Hi,
There is no such age limit assigned for iisc BS examination though they will allot students based on their scores obtained in JEE Main, JEE Advanced and KVPY examinations for which there might specific age criteria.
You can check about IISc from the link below
https://www.google.com/amp/s/engineering.careers360.com/articles/iisc-bs-eligibility-criteria/amp
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