Hilary Duff's Got a New Young Buck, Same Hot Beach Bod

Hilary Duff has a new young dude in her life, and he's already getting very familiar with her bikini bod.

Hilary was with the mystery man over the weekend on a Malibu beach. Don't know how long they've been together, but they weren't shy about getting physical in the water. Besides a makeout sesh ... they also did some surfing.

She's definitely got his back.

Looks like Hil's moved on from celeb trainer Jason Walsh, who she was dating this past Fall.