"He is achieving results I didn't know were possible at such a young age," said Cantwell, the Olympic silver medallist and a three-time world indoor champion. "The kid's good. I don't know if he'll ever be a senior champion. It is hard to tell because he is so young but to do what he's done at such a precocious age is amazing to watch.
"When I first watched him throw on video, I didn't know how the shot went anywhere. I think it's [his technique] terrible, but what the hell - the thing goes forever and that's all that matters."
The 30-year-old admitted he has doubts as to Gill's ability to win a medal at next summer's Olympic Games and believes the step up to the senior men's implement of 7.26kg presents a much greater challenge.
Gill's current personal best with the senior shot stands at 20.01m - some two-and-a-half metres shy of Cantwell's lifetime best and good enough for joint 46th in the world this year.
Of course, the fact that Gill is so high up the rankings in an event where often athletes don't peak until their late 20s or early 30s is a further indication of his rich promise. However, the American warns that neither the talented Kiwi nor the general public should expect too much too soon when he starts competing against top international senior throwers.
"When you are young the sky is the limit and I think he can throw really far, but how does he deal with stuff?
"You face all the travel, all the injuries, the expectations on yourself, and the expectations from others. You'll have them and they'll only get worse as you get older."
- Additional reporting, Steve Landers