Brake pads aren't what they used to be. In the "old days" of asbestos which were included in the pad, they'd go on forever. I'm new to Bimmers, but I'm not new to brake jobs. I live in a mountainous area in Vancouver, BC and I was going through pads almost once a year - crappier pads now, though I do know you can get better ones. 25,000 miles works out to be around 40,000 kilometres and I would be happy to get 40,000 Klicks out of a brake pad.
For the rears to go first is unusual in my experience, but my experience has been with FWD cars. The pads up front usually get the brunt of the braking task and are usually the first to go, with the rears following latter. I do wonder if somehow at some point they were dragging on the car.
I have a 2002 330xi and it has 24,000 Kilometres on it, so I know I will have to replace the pads in the next 10,000 to 15,000 kilometres, maybe earlier because of the steep downhill driving and braking I sometimes do here. Living in North Vancouver can be hard on brakes.