Dennis Quaid Screaming into 63rd Birthday with Hottie GF

Dennis Quaid got his birthday celebration started early with a serious check of the ole ticker involving his girlfriend ... and a roller coaster.

Dennis and model Santa Auzina -- who's 30, btw -- hit up Six Flags Magic Mountain over the weekend and strapped themselves in for high-speed fun, and a lot of screaming.

He'll turn 63 on Sunday.

If the ride doesn't make him feel young, something tells us Santa will.