Section 28(1)(a) in The Delhi Police (Appointment & Recruitment) Rules, 1980
(a)Ex-servicemen and ex-members of ail Police forces of State or Union Territory, who were paid from the Central/State revenues may be re-enlisted as constables' at the discretion of the appointing authority if their discharge certificate shows previous service as Good or of higher classification, provided that (a) they present themselves within two years of their previous discharge, (b) they conform to the physical and educational standards laid down for recruits from open market, (c) they are medically fir for police service according to the standards prescribed for recruits and (d) their age on the date of re-enrolment is below 30 years. The age limit prescribed in this para may, in special cases, be relaxable upto 40 years by the Commissioner o Police.