Young recently made his Senate campaign official, as did former U.S. Attorney Matt Whitaker (R).
Rep. Bruce Braley (D-Iowa) is Democrats' likely nominee for the seat being vacated by retiring Sen. Tom Harkin (D-Iowa).
"He's been loyal to me, he's been a good chief of staff for two senators and I hated to see him go, but if I can have a Republican colleague I want a Republican colleague," Grassley continued.
"I didn't encourage him to go but he wanted to run and I know his work, you know."
Some Iowa Republicans have expressed concern about their crop of candidates in the state.
Grassley pointed out, however, that neither GOP candidate in the race had a voting record to pick through, calling it a "significant advantage."
He predicted the race will hinge on whether the eventual nominee can catch up with Braley's fundraising advantage, admitting Democrats will be "way ahead of us on money."
He also said the GOP had a shot at winning the net of six seats they need for control of the Senate — but predicted it would be close.
"I think we have a chance of picking up lots of seats," he said. "I think it will be a very narrow majority if we have the majority."