What mileage does my car need to be to replace brakes?
When should you replace brakes?
Brake wear is dependent on how you drive. It's different for everyone. Have your brakes inspected at your local dealer not a brake shop. Brake shops are notorious about giving you a low estimate then "finding" a lot of other problems.
Also when driving or braking (could be only for a moment when you brake) if you hear a slight or pronounced squeak you need to take your vehicle to have the brakes inspected. The time for routine brake replacement should be mentioned in your owners manual, but I agree with Mayer it is very highly affected by the way you drive and the environment you drive in. I found that driving in the north I replaced brakes for the same vehicle twice as often as in the south.
Take care having brakes inspected at a dealership. With the downturn in the automobile market some dealers tend to take advantage of those who look and/or act worried. (my mom found this out the hard way when a dealer tried to charge her $450 for a brake job and a replacement disc, thankfully she called me and I told her to call another dealer for their price on having the brakes replaced and a disc, the price was $320) She called the first dealer back and told them she would be in to pick up the car and go elsewhere. So if they give you a pricey estimate, find out exactly what they are doing and shop around between dealers (if that's an option for you in your area)