04/30/2008 AT 11:20 AM EDT
Susan Sarandon looked as lovely as ever while strutting the red carpet in a clingy Donna Karan dress at the London premiere of Speed Racer.
So what's the 61-year-old's secret to eternal youth?
"I think it's mostly my kids who keep me young," she told PEOPLE, adding that she also does regular cardio and weight training. (Sarandon has one daughter, Eva – by director Franco Amurri – and two sons, Jack and Miles, with her longtime partner Tim Robbins.)
"I hope by the time you're 30, you ... stop worrying about how you look and try to worry about the kind of person that you are," she added. "It's more productive to learn how to live you life and to be joyful than to worry about if your thighs are getting fat."
And while she's "not against" plastic surgery, the Oscar-winner said she is opposed to the fear of aging that drives people to take extreme measures, like "exaggerated lip plumping."
"You can see I haven't had Botox [or] these things would be gone," she said, pointing to her frown lines. "I can't afford to have my face not moving."
In the end, Sarandon thinks her more natural look could be the secret to professional staying power.
In a few years, "I'll have an advantage of being the only one who looks 60," she said with a laugh. "Everyone else looks so much younger. [I'll] probably get all those parts!"
Reporting by MARIANA GREBLER