Ddawn's suggestion to see if they are fertile, which is a good one, is for eggs you have not yet tried to incubate. Once they have gone through incubation, the yolk pretty much falls apart if you crack the egg, so just try it on fresh eggs to see if they are fertile. That bull's eye might be on the bottom of the yolk when you crack it, so you might need to gently turn the egg over with a spoon to find it.
You can crack open the eggs that did not hatch after incubation to get an idea what might have happened. These sites tell you what to look for and what they might mean. As you can see, there are a lot of problems that can cause poor hatches, not just fertilization.
Mississippi State Incubation Troubleshooting
http://www.poultry.msstate.edu/extension/pdf/troubleshooting_incubation.pdf
Florida Incubation Troubleshooting
http://edis.ifas.ufl.edu/aa204
The ratio of roosters to hens in hatcheries to produce fertile eggs is about 1 to 10. This is for full sized breeds. In bantams, they use a bigger ratio but I'm not sure what it is, somewhere around 1 to 12 or 15.
Not all roosters are created equal. Some are more active than others. It's just their personality. Younger ones are more active than older ones. In the commercial hatcheries, they replace older roosters with younger ones when the fertility rates drop.
Many roosters are able to keep a flock of 16 hens fertile, but not all can do it. Fertility is a possible problem with your hatch, but is not the only possible reason, especially with that young a rooster.
Good luck!
