The lifespan of brakes on a car depends on a variety of factors. First is the quality of the brake pads and shoes. Most cars have what are known as composite brake pads while high performance sports cars and supercars have ceramic pads, designed to cope with high temperatures.
In general, the cheaper the pads, the lower the quality and the shorter its lifespan.
A brake pad’s life is largely determined by where you tend to drive rather than how many miles you cover each year.
For example, someone who covers 20,000 miles a year mostly on motorways is likely to is unlikely to need to replace their brake pads before someone who does 10,000 miles annually in town - because the nature of stop-start traffic demands more from the brakes.
Some brake pads have sensors that activate a dashboard warning light when the pads wear down by a certain amount. A fall in fluid in the brake fluid reservoir is also a sign that the pads are wearing.
Either way, the pads should be inspected when the car is serviced.
The brake discs themselves are usually made from iron. The nature of their operation means they can’t be coated with anything to protect them from the elements, which is why a car that has been parked up for a few days in wet weather can have ‘graunchy’ brakes for the first few minutes of use.
A thin layer of rust builds up on the disc, but it’s usually quickly removed by the action of the pads.
However, prolonged exposure outdoors can lead to more extensive rusting. This may be cured by skimming the disc but complete replacement may be required.
Carbon-ceramic discs don’t rust and last a lot longer, but cost significantly more to buy. They come as standard on most supercars and are at their best when up to operating temperature.
Brake pads should be changed on both front/rear wheels at the same time. The discs should also be examined at the same time, but do not need to be replaced if in good condition.
However, brake pads should always be replaced when the discs are renewed.
Less powerful/older cars have brake drums and brake shoes on the rear wheels. These aren’t as effective as brake discs and pads and consequently last longer.
However, they still need to be inspected for wear periodically.