Mine lasted 50k, it will depend on the elements etc 3/4 years I would say for mild steel system.Get a nice stainless one and you will never have to worry again
I wouldnt worry to much about the millage - just double check the service history, wear parts (clutch brakes exhaust and CV joints) and make sure the car has been looked after and you will be well away. and to be honest the millage isnt that far off 12000 a year ish (and i think that is the average) so only a little above. At least you know most of the little annoying faults would have been sorted if they had popped up 60000 miles in a car with faults would drive you mad!