Joanna Gaines Says Having Baby Crew at Age 40 Made Her 'Feel Young Again'

When Joanna Gaines found out she was pregnant with her fifth child, the former Fixer Upper star was surprised, to say the least. But after welcoming baby Crew last June, she says that the now-9-month-old has changed her in ways she never could have imagined.

“I kid with people, ‘If you ever want to feel young again, have a baby at 40,’ ” she says in the latest issue of PEOPLE. “It’s brought this whole new thing for me where I’m a lot more laid-back. People joke that I’m the ‘Fun Jo’ now.”

Joanna — whose latest project is a children’s book co-written with her four older kids (Emmie Kay, 9, Duke, 10, Ella Rose, 12, and Drake, 14) — says that baby Crew has given her fresh perspective.

“I realized there has to be spontaneity, and schedules kind of go out the door,” she explains. “It’s like, ‘Hey, if I don’t get to it, it’s fine.’ I’ve just relaxed so much more, and it’s been fun for me.”

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Parents newsletter.

It also helps that Crew loves tagging along everywhere the HGTV star goes.

“He’s my little sidekick,” says Joanna. “He comes to work with me every day and goes to all my meetings. There’s literally a sign-up sheet because everyone wants to hold him.”

As for adding another baby to their brood in the future, “Heck if I know,” Joanna shares, shrugging. “I thought I was done, and then we had Crew.”

RELATED VIDEO: Chip Gaines on Having Another Baby with Joanna: “Don’t Be Surprised If No. 6 Is in the Cards!”

“But [husband Chip Gaines is] always joking that he wants him to have a little sister. No plans for another baby,” she says with a smile before adding, “but then again, we’ve never been planners anyway.”

Joanna’s new children’s book, We Are the Gardeners, is available now on amazon.com.

For more on Chip and Joanna Gaines, pick up the latest issue of PEOPLE, on newsstands Friday.