How Brooke Shields Found Body (and Bikini) Confidence at 55: 'Women Over 50 Are Not Done'

As Brooke Shields tells it, the idea of herself wearing a bikini at 55 really began with her teenage daughters.

"I was wearing those big bathing suits that had as much fabric as possible," she tells PEOPLE. "My daughters were like, 'Mom, it's ridiculous.' It was sort of seeing myself through their eyes and just celebrating things like my butt. Things I just would never want to focus on in my life. Being 55 and saying 'Wait a minute, women over 50 are not done.'"

"If you're that age, especially if you are an actress, it's like 'you've had your career, relax,' but I think I'm just starting."

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Newly signed with powerhouse agency IMG Models, the actress and beauty icon talks about her "fresh start" and a few other life lessons in this week's PEOPLE.

Take her workouts for example. "I used to get fit doing Broadway shows eight times a week but I always did it for the show or for the job because the camera is not always kind," says Brooke. "So there was a vanity reason. I never knew I could find a place of peace that did not deal with outside appearances."

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Once in lockdown with her husband producer Chris Henchy and daughters, Rowan, 17 and Grier, 14, (and with no access to a gym) she began posting her at home workouts. "My Instagram workouts were never meant to be a stressor," she says. "They're just accessible, and a way to have movement and endorphins. It's funny to do arm presses with two bottles of wines. We don't all have our fancy gyms at the moment but I can guarantee, if you do something for five minutes, it will be a positive."

"I was never skinny," she notes. "I was always athletic which means you don't fit in the sample sizes. My daughters say I'm curvy. To them curvy is different. I watch them celebrate it. I'm learning from them and they always say you're better off with something that shows your body rather than a muumuu."

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And so with her daughters advice in mind, she began posting some bikini shots that revealed serious biceps-- and defined abs.

"Listen, I work hard at it. Every day, this summer I worked out. I kind of earned my confidence. I'm still going to get the right angle, mind you," she adds with a laugh. "And lighting."

Surprisingly, for someone so celebrated for her looks (and who had her first modeling gig at eleven months old and who made headlines for her Calvin Klein ads at fifteen years old) Brooke often felt cut off from the rest of her body.

"I wasn't in touch with my body, it was not something I looked at," she explains. "I almost didn't want to know it existed. There was this virginity complex and then I was a model, mostly covers, so it was sort of neck up. All about the face and eyebrows. My way of approaching the subject was just not to think about it."

"I was in dance class and the teacher used to say 'Shields, why don't you look at yourself?' and I said 'I don't need to look at myself. Everybody does that enough.' He said 'Well, you're going to fall flat on your ass if you don't."

And she adds "I don't want to fall on my ass."

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It's a lesson she's been learning slowly over time.

Not long ago it was her trainer, Ngo Okafar, who helped her see the true meaning of body positivity. "My trainer said every day in the gym there are women in the best shape possible and they'll walk by the mirror and say 'Ugh, look at that.' And a guy will come by with a belly, and go 'Yeah.' He said 'You've been coming to the gym and you make yourself smaller. Stop it.' He just had a baby girl and he said 'I'm never going to tell my daughter to dim her light.'"

"He told me 'You've started to believe all your self deprecation.' And that was the basis for all my humor," says Brooke. "And it was like you're right. I don't want my girls to do that. Just think of how great it would be if we can all feel this larger than life energy."