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.
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