Jennifer Aniston head over heels for her younger man

"This is a whole new Jen," a pal of the actress tells OK!. "She's trying new things, taking a risk, and is game for getting out of her shell, living her life and trying to be happy."

A friend of John's agrees, telling OK, "She doesn't rush off and go on vacation with John, and she's made it clear she will not be a groupie at his shows."

Apparently, her hard-to-get attitude is working on the heartthrob crooner. "He was smitten with Jen and came to visit her on set," John's pal says. "They're actually working around her schedule more than anything!"

The friend adds, "Jessica Simpson texted John all the time, but Jen waits a few days to text him back. She hasn't stopped her life for him. She's fun and flirty, but hasn't outright said, 'I want you,' which is something John isn't used to."

Image WENN