All of this is so subjective... I mean, it depends if your body is optimized; lungs working perfectly (good cardio) and bringing enough oxygen to your brain and muscles, muscles used to cycling and being able to sustain the required effort, etc. It's just science after all. If you did your best and ended up with that result, it can mean that it's your current limit and it's OK. Can it improve? Of course, with determination, consistency and frequent rides. Ride, eat, sleep, repeat