Johnson's men are looking to bounce back from their 27-17 defeat in Perth last week in a game which the England pack dominated against their less-experienced opposite numbers.
Lawes, 20, replaces the experienced head of 36-year-old Wasps lock Simon Shaw but Johnson is adamant his rookie can stand up to the Test arena.
"No, his aggression is fine," said Johnson. "He tackles hard and carries hard. He's a naturally aggressive lad who has speed. That's what gets you across the gain line. He's very instinctive and a tremendous athlete."
And Lawes himself was also quick to vow he will keep his cool no matter what the Aussies might throw at him.
"I'm not a dirty player and I don't bite that easily," said Lawes. "If they want to try and get under my skin, fair enough. I'll hurt them legally."
Lawes and Youngs' selection represents a meteoric rise for the pair who were both playing in the junior World Cup this time last year.
But they will have their work cut out with the Aussies recalling star fly-half Matt Giteau and Will Genia at No. 9 for the Sydney showdown.