Former Geelong coach and now Essendon assistant Mark Thompson believes it's somewhere near three years for a young player to be confident in what's expected of them.
But McCartney told radio station SEN on Friday morning that that figure was somewhere nearer the five-year mark.
"I think three years is probably the minimum for the really quick learners," McCartney said. "I think most take a bit longer than that."
"Three is minimum. I think it's more like four or five."
McCartney said Jackson Macrae, the No. 6 pick in last year's NAB AFL Draft, was ahead of the curve in his first season at the elite level.
"I've seen young Jackson Macrae learn things and show brilliant decision-making around the ball way ahead of a lot of other young people I've seen, which all goes well for him," he said.
On the other hand, Christian Howard, the No. 15 overall pick in the 2009 draft, has taken a little longer to develop.
McCartney is still confident that the 22-year-old will find his way.
"He's got a couple of things to work on, just around his consistency, but he has missed a lot of footy," McCartney said.
"He may just be the classic slower developer, too, he's got a bit of work to do but we're up for the fight with him and we think the end product might turn out pretty good."
McCartney said it can be difficult for young players to perform in a high-pressure environment, where the expectations are plentiful.
"Some just don't learn as quickly as others and some bind themselves up in the stress of the game and they put themselves under more pressure than they need to be," he said.
"I think some of our youngsters are at that point at the moment in that they're putting more burden on themselves than they need to."
McCartney also touched on the topic of Adam Cooney and his ongoing contract talks.
As reported by AFL.com.au earlier in the week, negotiations between the club and Cooney have reached a "stalemate".
But McCartney is confident things will fall in to place.
"I think you'll find that it'll play out quite comfortably and it'll get done in time," he said.
"But I think people have got to remember that contracts are still business decisions and there's two sides to the argument.
"There's always the person and their career and what's best for their family and there's the club element, too, and that's where list managers and footy managers get involved.
"For me, the number one priority is making sure that the player is clear, he's settled and he's very clear about our expectations and then the club take over from there."
Ben Guthrie is a reporter for AFL.com.au. Follow him on Twitter @AFL_BenGuthrie
