depends on conditions of how and where you drive. If you do city driving you will wear out the pads quicker than if you do country higway driving.
Thats why its part of every service to check.
Though on average its usually around 75-90k they need doing.
autos will generally chew pads faster than a manual....
but there is no "how many k's before i change them" crap....have a look at them! its the only way to tell......unless there is a grinding noise when you slam on the picks.....then you know there isnt much left...ha ha ha ha
I managed 65k on mine, but need to replace the rotors as they were warped. Went the whole hog, cross drilled and slotted with Bendix ultimates. Feels like a different car now, with a much better pedal feel