Eligible candidates for appearing in UPSC exams typically must meet certain criteria, including age, educational qualifications, and nationality. Generally, candidates should be at least 21 years old and not older than 32 years, with specific age relaxations for different categories. A graduate degree from a recognized university is mandatory. Furthermore, candidates must be Indian citizens or subjects of Nepal/Bhutan, or individuals of Indian origin who migrated from other countries. It's vital to check the latest notifications by UPSC for updates on eligibility criteria as they may vary for different exams.