Marc Anthony Rebounds with 21-Year-Old Hot Model

Marc Anthony's outdone himself again and wasted NO time doing so -- he scored a model barely old enough to order Jägerbombs, even before his divorce was final.

We're told the 48-year-old singer's been dating Wilhelmina Miami model Mariana Downing for a couple months now after meeting her at a dinner party. Witnesses say Marc was immediately smitten -- because he has eyes -- and they exchanged numbers that night.

We're told he called Mariana the next day and they've been together ever since. She's traveled with him to one of his shows, and they've vacationed together in the Caribbean.

Marc's divorce from Shannon De Lima was just finalized on Monday, but he's been on the market since they separated in November.