I have RIR , BO and australorps all the same age, 6 weeks . My australorps are taller and bigger than the the BOs and RIRs too . According to the Henderson breed chart, the australorps are early maturing and the BOs and RIR are moderately early maturing, so I'm thinking the australorp girls just grow faster. It says both RIR and Aurstalorps 6.5 lb. hen ( and the buff orps it says 8 pounds , but they are littler than the lorps too !)
