He also insists their April 29 date at Wembley has not come too early in Joshua's career and does not want to hear claims to the contrary after the event.
Klitschko and Joshua are expected to attract a post-war British boxing record crowd of 90,000 when the latter makes the latest defence of his IBF title and and when they will also fight for the WBA championship last held by Tyson Fury.
They meet amid suggestions that both Ukraine's Klitschko, at 41, is in decline and that Joshua may still be too raw to overcome the finest heavyweight champion of the past 15 years.
Many of those predicting victory for the 27-year-old Joshua do so on the basis of his exceptional punching power and athleticism, both of which they believe will be too much for his decorated challenger.
However, the flaws he has previously shown means comparisons have also been drawn with the popular, but at world level limited, Frank Bruno, and Klitschko expects that one-dimensional streak to undermine him.
"AJ has a lot of energy, he's young, he wants to show it," he said. "He has these big muscles that give him confidence. He wants to demolish people right in front of him.
"Those muscles give him a lot of confidence.
"But did you hear about boxing? It's the sweet science. Otherwise Johnny (Nelson, the retired cruiserweight sat near Klitschko) would have done the same thing, he would have been pumped up like that.
"Every other person would have been like that and would have smashed people.
"Boxing is the sweet science. The ice is thin. The most vicious boxers were conquered.
"I have a lot respect for Anthony and what he's doing. His commitment and physical ability - he can box, he can lift weights, he's strong. He can be a crossfit world champion actually.
"He has great capability. I believe he could do it. There are a lot of boxers doing it, but crossfit is not boxing."
Asked if Joshua had made a mistake in agreeing to face him in only his 19th professional fight, having not previously fought beyond seven rounds, Klitschko responded that there could be no excuses for either fighter.
"A mistake?" he said. "No. I'm sorry, should I wait another five years? I can't. The opportunity is now, everything has its time.
"I don't want to hear, 'Oh it was too early for him', or that 'Klitschko is over the hill'. He wants to become a billionaire, which is a great ambition. The question is before the tax or after the tax?
"I'm very critical of myself, probably the most critical man in the team. At 41, I'm still raw. He is in a certain way. He's improved, he's accelerated a lot, but he's still raw.
"We have seen a marked improvement and we will see on the 29th of April more improvement. I hope both fighters get through it injury-free, so there are no other issues."
