Amanda Seyfried Elle magazine Anniversary issue cover watercolor print halter top

Amanda Seyfried is one of four Elle October issue cover girls. Photo courtesy of Elle Magazine

How do you celebrate a quarter-century of fabulousness? With a little help from Hollywood hotshots like Amanda Seyfried, Megan Fox, Lauren Conrad, and Gabourey Sidibe.

Each beauty graces her own cover of Elle magazine's October/25th anniversary issue, which spotlights 25 superwomen in the 25-something age range, all photographed by Carter Smith.

"Dear John" star Seyfried, looking flirty on her cover in a Louis Vuitton wool halter dress with a watercolor bodice and plaid skirt, turns 25 in December, and although she's in a good place in life, she's already fretting about the future.

"The best thing is, I'm happy," observes Seyfried, who poses Twiggy-style for her feature in mod makeup, a Lisa Perry clear vinyl rain jacket, and a Chanel red-checkered cashmere sweater with matching bikini bottoms.

"The worst is that I'm scared; the scariest thing is that I know it can't be easy -- the years to come."

Fox, meanwhile, already finds life to be a challenge.

"When I talk about my husband [Brian Austin Green], I feel as if people roll their eyes," says the 24-year-old "Jonah Hex" star, who appears demure in minimal makeup and a nude-colored dress on the cover before revving things up inside with dotted Emporio Armani Underwear and an unbuttoned oversized Armani Jeans striped shirt.

Lauren Conrad aviators suit Megan Fox striped button-up shirt leopard print underwear Elle Magazine Anniversary issue

Lauren Conrad (left) and Megan Fox (right) in Elle's 25th anniversary issue. Photos courtesy of Elle Magazine

"It's like when you're 16 and order a martini, and the waiter says, 'Do you think I'm stupid?' They can't grasp that I'm old enough to be married."

Conrad, whose cover attire is a colorful jumper, makes it clear, however, that at 24, she's in no rush to settle down. "I was never that girl who just wanted babies," says the reality star/designer/novelist, who, inside the magazine, looks very Lohan in a gray Gucci blazer with matching pants and Ray-Ban aviators. "I wanted a career before all of that."

And for 27-year-old Sidibe, being in your 20s is all about having fun -- even if it means lying about your age.

"Part of me thought it would be weird if people knew I was a grown-up playing a teenager in 'Precious.' So I had a twenty-first-birthday party," the "Big C" star, who wears a green Tadashi Shoji jersey cocktail dress with Fenton jewelry for both of her shots, says of marking her big two-five. "We had drinks and went to a strip club called Shotgun Willie's."

For more of Elle's favorite 25-somethings -- including Mila Kunis, Lauren Bush, and Camilla Belle -- pick up the new issue and visit the website.

In related news, check out Eva Mendes's loopy photo shoot for Vs. magazine.