Hey Karen, I would say that at 104,000 miles it should have been done by now and as Piotr said the cambelt s are normally changed around every 5 years but it can be between 5-7 depending on the engine, vehicle age and mileage.
Usually they are changed around 50k-80k. Again this depends on the engine. If it's not been done then you'll want a discount as this will cost you around £400-£500.
If it has been done then the dealer should have proof of this.
Hope iv helped :)
cheers
steve