The original Scrubs cast felt old acting with people who were "freshly out of the womb" when the original show aired

Speaking to PEOPLE magazine, Donald quipped: "You really don't realise you're old until somebody reminds you of how old you are.

"To have someone say to me, 'I was freshly out of the womb when Scrubs started, and now I'm on the show with you,' was a little surreal. "It's a little like, 'Wait a second, I'm that old? I'm that old?' "

Zach admitted that while he obviously knew that the original series was shot over half a decade ago, it still "kind of blows your mind" to be working with people either weren't born for the first run, or were "literally infants".

He said: "I knew that we made the show in 2000, but I'm acting with these 25-year-olds who are brilliant and smart and clever, and then they say they were born in 2000, and it kind of blows your mind.

"It's weird when you're like, 'What? But you're my work friend. You weren't alive when we made the show?'" he continues. "It's weird when you do the math, it doesn't feel right."

Meanwhile, Sarah joked that she likes to believe she's still in her 30s, but the younger cast makes that difficult.

She quipped: "In your mind, you kind of still think you're 30.

"And we're not. It was actually one of the coolest experiences of doing the reboot was getting to work with the five of them."

The newcomers include Avan Bunn (Sam Tosh), Jacob Dudman (Asher Green), David Gridley (Blake Lewis), Layla Mohammadi (Amara Hadi) and Amanda Morrow (Dashana Trainor), and Sarah has been impressed.

She added: "They are as nice as they are talented, such interesting, fun human beings. And we had so much fun getting to know them, but also, they're ridiculously talented."