The club announced on Thursday it had reached agreement with Aston Villa to secure the services of the 25-year-old and Irwin is predicting a bright future for the England international.
"I think it's a great signing and I expect him to be a really good player for us," the Treble winner told ManUtd.com. "He's got good ability and is a real threat from set-pieces, which is something we've been missing in the last couple of years.
"He can play anywhere behind the front man and his delivery into the box is fantastic. He's got a real eye for goal too and, given the opportunity, I think he'll chip in with a few goals next season."
Young is United's second signing of the summer following the capture of defender Phil Jones from Blackburn earlier this month. And Irwin wouldn't be surprised to see a few more new faces before the transfer window closes.
"The fact we've lost Nev, Scholesy and Edwin, and Owen Hargreaves has also left, meant we needed to bring some players in because you need a big squad to be able to challenge for the top prizes. Phil and Ashley are really good acquisitions and I'm sure both will do well.
"I think there will be a lot of money spent in the next couple of months by a lot of teams and I wouldn't be surprised to see us bring in a couple more players."