She became a Hollywood star as a teen, but Uma Thurman – who turns 40 next year – says getting through the last decade was a big challenge.

"I can't say my 30s were the easiest time. And I had thought my 20s were hard!" she tells W Magazine for its October issue.

For those who think she had it all – the looks, the career (Oscar and Golden Globe nominations), and the family (kids Maya, 11, and Levon, 7) – she has a warning: "You know, that's the worst mistake a woman can make, to think, 'Oh, I'm 32 and I've had two kids and I've worked since I was 16 and now it's going to get easier.' Because as soon as you think that, you're doomed! You're absolutely doomed!"

While Thurman was busy raising her kids (she and their dad, Ethan Hawke, divorced in 2004) she limited herself to mostly New York-based projects so she could be close to home. As a result, her career slowed down.

But now that the kids are older, she says she's ready to "slightly selfishly" focus more attention on acting. "I am a mother, but I need to do what I'm good at doing," she says. "Even your kids need you to be who you are. I've been living at home for work for a long time. If I don't leave soon, I'm going to literally choke my career to death."

Her new priorities also mean she isn't focused on planning her wedding to fiancé Arpad "Arki" Busson, a London-based financier.

"I'm happily engaged, but we haven't set a wedding up," says Thurman. "I'm not in a rush to do anything. One day we'll do it, when we're ready. We can't live anywhere else because my children's father lives here. We'll figure that out."