Since no one from Kentucky has answered your question, I'll give it a try.
It probably depends on what time of year your county and state fairs are, and what their weight limits are. Most steer shows don't have any specific age rules these days, weight is what matters. Most calves that age are going to finish out at around 18 months, so your calf is probably ideal to show as a market steer in the spring of 2018. If he's big, you might be able to get him to market size by fall of 2017 (when he's around a year old), but if your target shows are market shows in the summer of '17, he probably won't meet minimum weight requirements for a market, but could show as a prospect or feeder if they offer that division. If your shows are in the summer and he's not too big you might be able to hold him over for summer of '18.