I have a 52 plate cup (19k miles) and ive got quite a bit of rust there.
I even had corrosion on the inside of the front discs (apparently caused by the car sitting on the forecourt not being moved) I took the car back to the dealership and they changed the discs and pads for free
They said that the corrosion everywhere else was relatively normal.
But if i were you i would let them take a look. It is worth checking out, especially cos the car is reasonably new and is still under warranty.