Sharon Stone Celebrates 60th Birthday with Miami Beach PDA

Sharon Stone's turning the big 6-0, but don't get hung up on numbers -- she sure didn't during a South Beach PDA sesh with her, apparently, much younger bf.

Sharon's down in Miami for her birthday, which is Saturday, but she pregamed Friday afternoon in the arms of the shirtless mystery dude.

No word on who he is, but she's been hanging out with him since, at least, January. Based on the kissing and caressing going down on the beach ... they're VERY cozy with each other.

Ya gotta love it -- at 60, she's still trusting her basic instinct.