Yes you can apply for civil service examination of UPSC at the age of 30 year as on 1st august of examination year. OBC and ST/SC candidates get age relaxation for this exam .

Age limit :
21-30 years as on 1st August of the year of Examination.
OBC candidate age limit maximum : 33 years.
SC/ST have 5 years of age relaxation.

IAS exam Eligibility Criteria:
Minimum You must complete graduation in any discipline from a well recognized university.

Important dates :
Civil Services Preliminary Exam 2014
Notification Date : 17th May 2014
Last dates for Applications : 16th June 2014
Examination will be held on : 24th August 2014

Civil Services Main Exam 2014
Examination will be held on : 14th December 2014