At what mileage should I replace brake pads and discs?

My Mazda 6 is just under three years old with 24,000 miles on the clock. I was told that the pads and discs need to be replaced all round. My first service at 7200 miles noted 8mm on the pads, the second service at 15,800 miles noted 7mm wear. A year later, I'm getting a grinding noise off the back brakes and rust on the alloys. I'm not hard on the brakes, using the gearbox in conjunction with the brakes to slow down. What mileage should I expect to have to replace pads and discs on a Mazda 6? My last car was around 60,000 miles when this happened, and from what I can see on the net, that's pretty standard.
Rear brakes fail before the fronts because all brake discs rust all the time the car is standing, but because 95 per cent of the car's braking is at the front the rust gets cleaned off in use much more effectively at the front than at the back. Very common for rear discs and pads to need replacing first. But Mazda are starting to get a bit of a reputation for this.
Answered by Honest John on

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