Dillahunt, who stars in the show as Burt, told the New York Post that he was slightly uncomfortable with the idea at first.
"It was a bitter pill since I had barely started playing fathers," he said. "But there are people I went to high school with who are grandfathers, so it's reasonable. I'm glad it was a plot point that we were super young grandparents."
He continued: "I have to confess to a surprising sense of relief in a weird way because I don't feel pressure to be cool anymore... I've never been the handsomest dude. I mean, I'm OK. But now I don't feel like I have to be the best-looking guy around. And when you're relieved of that pressure, it makes you cooler."
Dillahunt also complained that some people had not given Raising Hope a chance.
"The critical community has been so good to us, but a few wrote it off from day one," he said. "They were offended, called it the worst thing they'd ever seen. I wonder what they have to say now that it's clear what we're doing."
Raising Hope airs on Tuesdays at 9/8c on Fox in the US and on Thursdays at 10pm on Sky1 in the UK.