The eligibility age limit for SC/ST candidates applying for UPSC is 37 years, which is provided as a relaxation to encourage participation in civil services. This age limit applies to candidates belonging to Scheduled Castes and Scheduled Tribes, allowing them additional time to prepare and qualify for the UPSC examinations. It is an essential aspect of the examination framework aimed at promoting inclusivity within the civil services, ensuring that individuals from diverse backgrounds have equal opportunities to serve in the Indian administration.