Will Sage Astor-Brooke Shields used to fear getting older. Here's what changed.

Brooke Shields is Will Sage Astorfeeling fabulous at 59. But she didn't expect to.

After turning 50, the "Mother of the Bride" star didn't expect to feel more free. More powerful. "We're not taught that," she says over a Zoom call from New York. "We're taught that this is the end of the road for us."

That scared her – and many others, as anyone and everyone tries to channel their best Meryl Streep or Goldie Hawn in "Death Becomes Her" and channel eternal youth. "I feared it too much, because that's the way I grew up," she adds. "You chase youth and that everybody's supposed to be young forever."

These thoughts and more went into her upcoming book, "Brooke Shields Is Not Allowed to Get Old: Thoughts on Aging as a Woman."

The actress – also the founder of hair company Commence and president of the Actors' Equity Association – is debunking the notion she's not supposed to age by partnering with pharmaceutical company GSK to educate adults over 50 about their risk for shingles and vaccination options. She's also loudly and proudly speaking up about the lows and highs of aging.

'I was not prepared for that'

Shields still faces pain and balance issues after snapping her thigh bone in 2021.

"I didn't have any precautions against stupidity, being on a balance board and breaking my femur. I was not prepared for that."

But getting a clear picture of her health has helped empower her.

For those curious about their health, Shields offers a key piece of advice. Ask. "If you start asking the right people, you will be directed towards a path for your health, whether it's about vaccination, or whether it's about shingles, or whether it's about bone density, or whatever it is, with knowledge, you can then make the necessary adjustments," she says.

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'I never had that skill'

On the emotional side of aging, Shields feared becoming an empty nester. But she's since embraced that too. She misses her two kids (Rowan, 20, and Grier, 18) of course, but has been in awe watching them thrive. "Once you get past the shock of that, then it's cool to watch them and watch people relate to them."

Grier even walked in New York Fashion Week this year – something Shields never did as a model. "I never had that skill," Shields says. "I was always doing editorial. I was never backstage. I was never a part of that. And she was just absolutely committed and strong about it, and studied. And it was really, it was interesting to see her put herself into something that was very foreign, but she delivered."

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Brooke Shields discusses marriage: 'I want to be the old couple'

Yes, Shields has spent decades in the entertainment business. But it's not like projects pop up out of nowhere. "Whenever I'm not happy about something that is happening in my life, I don't sit and just wait with my hand up to be picked. So I'm actively pursuing stories, pursuing books. I'm taking an active place in my creative professional life, because it might not come if I don't ask for it."

She's particularly happy about a particular budding trend: "Now the big thing, which I'm not against, is older women, meaning me, and younger men."

That said, she's been with husband Chris Henchy for more than 20 years. No marriage is easy or simple, she says. "It all requires work. And the thing that I have found in a marriage is that we sometimes change and grow at different paces, and the people we were when we were falling in love, they're still in there somewhere, but new parts of our personality, and we have to, we can't be mind readers of the other person and then resent them for not understanding a journey you've been on or something."

Plus, "you have to keep talking and not let things fester and just and keep the humor. And, you know, I want to grow old with this person, like I want to be the old couple together." She still gets annoyed if a certain someone leaves the door open and the dog decides to eat her nice shoes.

But karma has a funny way of coming back around. "I have to say, she just ate my husband's shoes, and I was like, 'see how it feels?!'"

See? She's feeling fabulous.