I think so much of it depends on your natural fitness, your weight, and your general current state of fitness.
Since that 41:53 was your first 10k, once you've ran a couple of 10k's you'll know what sort of pace you're capable of off your current training (e.g. you might find you can run a 10k tomorrow in under 40mins) - from there you'll get a much better idea of what you need to do in training to achieve your targets.
That said - its by no means an unrealistic target at all. Your biggest gains will come when you first start running and training regularly and then as the times drop it'll become a bit harder to shave time off those PB's.
Keep us updated though with your training and any races you do... I'll be very interested to see how you progress!
