But he also sounded a warning over Osei-Nketia.
In other words, the 1.9m teenager, who attends Scots College in Wellington, is already a big unit and about the same size as All Black wing Rieko Ioane.
Keddell told Radio Sport's Jim Kayes that if the 17-year-old Osei-Nketia keeps growing, he may have to consider one of the many other sporting options available to him.
"He's nearly 100kg whereas most sprinters are 75 to 80 kg," Keddell said.
"You just don't know. Maybe the guy grows another three inches, and reaches 110kg.
"He's then going to struggle to run under 10 seconds and that's it, he has to be a rugby player or an AFL player or an NRL player. Maybe the Americans have a crack at him.
"I've never watched him play but seen highlights which show him busting through lines, scoring 70 to 80m tries or running around people. It's pretty impressive.
"The fact he can run that fast at that age is impressive, the face he's the size of a rugby player and can do it is the bit which is a bit scary.
"The fastest rugby player in the world is (American) Carlin Isles at 10.13s. I'd put money on it that Eddie would smack him up at 100m.
"I was fast as a kid but a terrible rugby player. But I scored a lot of tries - speed is a beautiful weapon when you play rugby."
While Osei-Nketia is slow out of the blocks, Keddell said that was a natural consequence of being so tall and was something to work on.
The legendary Usain Bolt, another tall man, was called a slow-ish starter but Keddell said he actually had an "amazing start" relative to his height.
But athletics could be a fragile business — "there are no givens". Qualification times were lower, fields smaller. Conditions needed to be right to get the great times.
Rugby talks had been with the national body rather than individual Super Rugby franchises. He confirmed approaches had been made by NRL and AFL clubs. There had been chats with New Zealand athletics.
"It's really flattering, all the people wanting to be involved," he said.
"We've got managers from America emailing saying sign this, we've got a big deal from Nike for you.
"A lot of people jump on the bandwagon with a young kid."
Keddell said Osei-Nketia had always wanted to run and play rugby for New Zealand rather than Australia, where his family has lived for the past eight years.
"We've just got to lock a few things in," he said.
