She's 42?!

Supermodel Heidi Klum continues to prove that age ain't nothing but a number, looking enviably fit in a white two-piece bikini in St. Barts on Monday. Sporting a trucker hat and shades, the "America's Got Talent" judge looked super-youthful while spending some time in the sun.

PHOTOS: Hollywood's Hottest Bikini Bods

Heidi actually celebrated her 42nd birthday on Monday, going on a romantic vacay with her boyfriend, 28-year-old Vito Schnabel. Heidi and her new man, a New York art dealer, certainly had no problem showing a whole lot of PDA on the beach.

Heidi and Vito began dating last February after she split with her bodyguard, Martin Kristen, in January 2014. Vito’s actually no stranger to May-December romances, having been linked to Demi Moore, 52, in 2012.

So what's Heidi's secret to a flawless bikini bod? Apparently, it's all about moderation for the mother of four.

"I like to stick to fresh fruits and vegetables and lean proteins," she told Glamour magazine last March. "It's important to keep a balanced diet, but I'm not a fan of deprivation. If I want a cheeseburger, I am not only going to eat that cheeseburger, but I'm going to enjoy that cheeseburger."

WATCH: Heidi Klum Gets Reporter to Strip Down to His Underwear