Hi Neerja, as per their official website, the conducting body of ugat exam, AIMA has not mentioned any score eligibility criteria for writting the exam. He should have completed 10+2 exams from a ugc approved institute. Hence he is eligible to apply and appear for the exam. For further doubts, please refer this link of the official exam, 

https://www.aima.in/testing-services/ugat/information-to-candidates-for-ugat.html