Age ain't nothing but a number!

Paul McCartney and his wife, Nancy Shevell, escaped the cold this holiday season and are currently enjoying themselves in St. Barts. Shevell, 56, flaunted her toned bod in a green bikini while the two took a PDA-filled stroll along the beach on Sunday.

Check her out showing off her impressive abs during their romantic getaway.

PHOTOS: Hollywood's Best Bikini Bods Over 40

Shevell -- who serves as vice president of her family's transportation conglomerate, which is reportedly worth nearly a half billion dollars -- married 73-year-old McCartney in October of 2011. The two have been dating since November 2007.

The brunette beauty is the legendary musician's third wife; McCartney's first wife, Linda Eastman, died of breast cancer in 1998, and he split from his second wife, model Heather Mills, in 2006 after four years of marriage.

WATCH: Uma Thurman, 45, Puts Her Slim Bod on Display in Adorable Retro Swimsuit in St. Barts

Watch the video below to see eight more celebs whose third marriage seems to be the charm.