I am in agreement. He is at the age where this behavior is common. It is very unlikely he would get head shy from a good bump in the nose for correction and he is young enough it should be a quick and easy fix. If it is not corrected it will not take long to become an issue - he will get bolder and bite harder and it will hurt! Even young horses with proper herd socialization will take a nip at humans because they learn to establish a place with us as well.
Part of responsible horse ownership sometimes involves a firm hand. That doesn't mean an abusive hand by any means but, it is my opinion you cannot properly or safely care for a horse that walks all over you, the vet, or the farrier. If you watch herd behavior in the pasture it's easy to see that your hand will not inflict what a hoof or bite from a pasture-mate would.
Watch his body language and beat him to it (just before he nips) if you can - as soon as you see it coming. A good firm one on the nose - and act like nothing happened. It will not take him long to realize it's not okay and the nipping should stop. Aggression in horses towards humans is fairly rare, especially at his age.
Best of luck :)