Fergie said: "There is no doubt that at 21, it is another three years before you get anywhere near your maturity.
"When you are 21 you do inconsistent things - you score a goal, you miss a goal. There is nothing consistent about you but these two maybe defy that."
Ferguson is not just expecting great things from his star duo this term. He also feels the whole squad will benefit from last term's triumph.
And the Scot is aiming to take his title medals into double figures by May 11 next year.
Fergie, who won the league for the first time in 1993, believes that feat would never be matched again.
He said: "It would be fantastic to win it 10 times - especially for someone like Ryan Giggs.
"That would be a tremendous incentive and I wonder if it could be done again by a player or manager. The challenge is more for the players, though."
But Fergie accepts it is part and parcel of his star striker's game.
The United boss admitted: "He will always have that.
"Wayne knows when he has done wrong so when he is unfairly treated, he reacts to it.
"You don't want him to do that all the time but at least there is an honesty about what he does."