It's only just run in at that mileage! :)

Air filters are a standard service item. As for discs, of course it depend how you ride, but mine are coming up to the design limit at 36000m! So I wouldn't have thought you need worry about that just yet. The minimum thickness is stamped on them. You can easily check it with a micrometer (a vernier gauge won't really do cos it'll measure the "lip" on the edge of the disc).