I think the issue is actually Shaun Johnston, he's 62, and playing 39 year old Michelle Morgan's grandfather. That's only a 23 year age difference, which seems pretty small for a grandfather.
And just out of curiosity, I looked up the actress who plays his daughter and Michelle Morgan's character's mother, who only appears briefly in the first episode and then flashbacks, and she's only 1 year younger than Shaun Johnston.
