As stars like Jada Pinkett-Smith, Winona Ryder, Heather Locklear and Camryn Manheim, among others, reach oh-no! birthdays this year -- that is, 30 and 40 -- and PEOPLE, in its latest cover story, reached out to discover the secrets behind their ageless sizzle. With Pinkett-Smith (30 on Sept. 18), it's a matter of attitude. "I'm finally feeling like a woman," she says. "Before, I was a little girl just trying to be a woman." Ryder (30 on Oct. 29) has achieved a beautiful, mature look with a no-muss, no-fuss regimen that includes doing her own hair and makeup for most red-carpet events, getting eight hours of sleep a night and occasionally consulting a nutritionist. Meanwhile, Locklear (Sept. 25) isn't dreading the four-decade mark at all. "Everybody makes a big deal out of it," she says. "You know what? I'm alive. I'm still around." Camryn Manheim (40 on March 8) doesn't fret about her age, either. In fact, for the past 15 years, she has actually advertised it on her personal cards, with the words, "Camryn Manheim. Since 1961." "I don't buy into the stigma of turning 40," says the Emmy-winning star of "The Practice." "I think 40 is the new 30. Most of the time I feel like a big kid."