Youngs was at the heart of England's historic second-Test win over the Wallabies last month, scoring a sensational individual try and bringing out the best in a previously cumbersome-looking backline.
And Lions legend McGeechan, who has been a coach with the world's most-famous touring team on no fewer than five occasions, admits that the affable youngster would have made the latest Lions tour to South Africa had it been scheduled for 2010 rather than 2009.
"Sometimes making just one change affects the way others play and I think Johnson's decision to play Ben Youngs was critical for England," McGeechan told the Daily Telegraph.
"The way Youngs played had an impact on what happened around him and that drew slightly different games out of other players.
"He has really impressed me and if the Lions tour was this summer I probably would have brought him."
Perhaps surprisingly given their struggle for form in recent years, McGeechan believes the post-Lions emergence of bright young players such as Courtney Lawes, Chris Ashton and Youngs means England are currently in the best shape of all four Home Nations.
McGeechan, whose Lions involvement has seen him work closer than anyone with the best players Britain and Ireland have to offer, is impressed with England's current mix of youth and experience.
The former World Cup winners haven't claimed a Six Nations crown since their historic global triumph in 2003 but McGeechan is confident that Martin Johnson's men are on the right track for game's global showpiece in New Zealand next year.
"Youngs is one of a number of younger players that have come through and got the experience of winning in the southern hemisphere, while England Saxons also did well in the Churchill Cup," added McGeechan.
"England, of all the sides at the moment, have probably got the best mix of established, experienced players and enthusiastic, quality younger players.
"If that continues to evolve over the next 12 months then they will probably be in pretty good shape for the World Cup.
"Johnno knows what he wants and he knows what it takes to create a winning environment.
"The key is for him to see that what they achieved in that last Test against Australia as just a starting point rather than a finishing line.
"England need to say, 'Right, that is what we have to hold on to now. Where do we want to go next?'
"When a World Cup comes around, you just have to be there or thereabout as a team, with the right players fit, and then you get momentum in a tournament.
"England definitely suffered last November with injuries. But most of those players are fit again now and that gives Johnno a core group to develop, while I think Lewis Moody has also done well as captain. They look in good shape."