Narrow heads are common with hatchlings that come out a bit early and generally goes away fairly quickly.
Small heads can be a result of overfeeding when young and will also go away with correct feeding and snake growth.
The duck billing can be a result of super black pastels and cinnamons - don't think that changes much with age or growth.
Head shapes do vary and there is no established "best shape" really, as long as the animal is healthy and able to breathe etc I can't say it bothers me.