Wear depends heavily on driving style, as they like to say at the tire store. But fwiw, I have 14k miles and rears are past wear bars and fronts have at least 6mm left in the center (not to bars yet) but shoulders are well worn. I drive aggressively and have had some track time (only 3 days) and keep pressures adjusted regularly. Track time chews shoulders up very quickly. If all 4 of yours have the same wear pattern on the shoulders, autoX or track days are a real possibility.
Banner-Free since 8/3