Your post is a little confusing. You say you drive a 525 year 53, what is that? But since you reference the iDrive, it has to be a 2004+ 525. If that is not the case, correct me. In terms of the mileage in the iDrive until the brakes need service, it is an estimate that, if your driving style is relatively easy on the brakes, could move up some from the initial estimate. BMW starts the estimate at say 20,000 miles before brakes need servicing, but if you are easy on them and they are not wearing as quickly as expected the mileage estimate will move up. I wouldn't expect it ot go up too much, but it could move up. Certainly doesn't sound like a dangerous issue, but I would mention it to your Service Advisor one time to get their thoughts on the mileage change.