How long do brake pads last

System

The front pads you should be able to see or feel without needing to take the wheels off. Rotate the wheel so the gap between the spokes is where the caliper is. You should be able to see the metal backplate of the pad. See what the gap between the disc side of that and the face of the brake disc is if you can't see the friction material. Whilst it isn't ideal and doesn't tell you what the state of the inner pads are at least you'll have an idea if the tyre place say they need changing.