I think there is a correction, it should read as 60 yrs.of age (instead of 60 yrs.of service).
1.PS Banks have got their own gratuity scheme/rules, if so,some key parameters are required to compute.
2.Date of joining & last date of duty/date retired, last pay drawn, what is the gross salary as per gratuity scheme (some employers' scheme provide for average salary of the 12 months preceding the retirement), no.of yrs/no.of days worked in the terminal yr. etc. also required.
kumar.s.