Hello,
In order to appear for UPSC Civil Service, you need to attain 21 years age and complete graduation in any discipline from a recognized university, there's no specific aggregate required in this case, you can also apply in the final year of graduation. As you mentioned you've done diploma in mechanical engineering, you can complete your BTech through lateral entry in order to be eligible for UPSC, or you need to pursue graduation in any of your favorite subjects as eligibility of UPSC is based on graduation, and diploma studients can't apply for this.
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