Hi Shadia,

The eligibility criteria for IAS Exam is that the candidate needs to be at least 21 years old and should not be more than 32 years old. This age limits may vary with respect to caste reservations. For Other Backward Castes (OBC) the upper age limit is 35 years.

Given the fact you were born in 1991, you're still eligible for IAS exam.

Hope this helps.