When you regularly clean your brake pads an eternity. On my almost 8-year-old mountain bike with 15,000+ km on it (I would estimate), I am still on my first pair. They can get damaged if stone, sand or mud gets lodged in between, which then act as an abrasive. Under normal circumstances, your brake pads are the sacrificial part. I reckon it is much more common to have to replace a rotor after a crash where the rotor gets bent out of shape.
Squealing is usually a sign of dirty pads and rotors. You should clean both regularly with alcohol. If you haven’t cleaned them in a very long time they might also be contaminated, and you may have to replace them. (Pads are porous, so they soak up oil and grime like a sponge.) Or they have overheated and become glassy. Although I wouldn’t expect that to happen on a road bike very often.