Dennis Quaid's Ripped Beach Date with Model GF Santa Auzina

Dennis Quaid's not letting age slow him down ... instead, he's hitting a Hawaiian beach with his much younger gf, packing on the PDA, and showing off his ripped 63-year-old bod.

Dennis and model Santa Auzina had nothing but a good time Wednesday on the sand in Kauai -- hugging, kissing in the sand, and hanging with friends.

After a quick makeout sesh ... the couple hit the water for something called SUPsquatching -- which is basically paddleboarding, but with a group of people together on a huge board.

These two love to live life on the edge.