"Her body is insane. When she comes over for family Sundays, I'm like, 'Do not get in a bikini.'
My husband's always like, 'Kat, get in the pool!' And I'm like, 'Simon …'"
Erin said she believed the age difference has played a role in a positive way.
"Our dad comes from a generation where women are more passive. He is also passive about his feelings. Kat has really pushed him to open up.
"We could get into a fight, and then Kat's like, 'No, you have to pick up the phone, call your daughter back.' She's a facilitator, which is really important. She pushes him to be more emotional and more vulnerable."
Similarly, David previously described his 36-year-old wife as the "whole package".
The singer tied the knot with the 'Scorpion' star following a 12-month engagement, and he feels incredibly lucky to be able to call her his spouse.
He said of Katharine: "She's the whole package, you know? Singing, acting, beauty, she's got it all!"
Shortly after their wedding, Katharine decided to take David's surname because she loves the "traditional" nature of taking a partner's last name.
She explained: "I'm a romantic. I've always liked the idea that it's still a traditional thing that exists in our society. I like the idea.
"I think it's romantic and it's a great last name ... We've been away since we've been married, so not [yet], but I love it. I just love the ring of it, so I'm enjoying it."
