Salma Hayek proved age is just a number as she ditched her clothes while skinny-dipping in honor of her 60th birthday. The actress, whose birthday falls on Sept. 2, took to Instagram Monday to share sultry snaps of herself rolling around in the ocean. A second photo showed her posing with her backside to the camera as she played around with her hair. “60 and grateful,” Hayek captioned the photos. Several fans gushed over the “Frida” star, with one writing, “60 yet ageless … Father Time must be smitten with you 😊.” “60 years of sweetness, talent, grace, and a beauty that shines from the inside out,” another wrote. “60 years of making the…