One of our roosters is fourteen and still fertile. However, he can't keep up with as many hens as he used to. For your boy, you will most likely have to just incubate the eggs and discover if they are fertile, or not.
You should be able to visualize your egg yolks to see if he is still fertilizing your gals. If the majority of your eggs aren't showing that bull's eye, I'd replace him with a younger roo. You don't really have to get rid of him if he is an old friend, a new roo will finally assert dominance and the old roo will be second fiddle when it comes to breeding. If this doesn't happen, you may have to rehome him to a retirement farm or the stew pot.