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.