Sorry I do not know his age.
I have "heard" that there are a few Texas ranches producing 60" kudu bulls at 5-6 yrs old. I assume they are feeding high protein content supplemental feed similar to the deer industry. With all the available research and technology I assume they will shortly produce a feed just for these animals that will produce ludicrous horn growth. There are labs that test the spoor and the ruminant stomach samples and determine how minerals/protein is being digested and what is coming out, they will play the the formula until they figure out what the highest absorption rate etc. Not what the purist want to hear, I know, but it's the facts.
As for the prices, yes they are silly- but supply and demand and apparently there is no shortage of demand at these prices yet so.....