Don McLean's playing a young man's game, and dominating so hard ... he's already got a trophy.
The legendary "American Pie" singer was leaving a hotel Wednesday in London with his much younger, and total smoke show of a Playboy model girlfriend ... Paris Dylan.
We'll do the math -- she's 24, he's 72, which adds up to ... get it, Donnie!
He was dressed age-appropriately for an oldie, but goodie folk singer. Paris also appropriately rocked a curve-hugging dress. Even though she's posted pics with a shiny rock on her finger, Don's people have told us their thing is strictly professional.
Don didn't write the book of love ... but those legs gotta put his faith in God above ...