The high schooler who rubbed elbows with Travis Kelce during a sweat sesh in Florida over the weekend is raving about the workout ... telling TMZ Sports the run-in with the Chiefs star "was amazing."

Jazz Lewis -- the teenage son of NFL legend Jamal Lewis -- sat down with us just a couple days after he got in the workout with Kelce ... and he had nothing but nice things to say about the future Hall of Famer.

Jazz, who plays wide receiver for Chamblee Charter H.S. in Georgia, tells us Kelce gave him a whole bunch of pointers that he's sure will help him when he hits high school gridirons in the fall.

"I got to learn," the younger Lewis said. "He gave me some tips on how to run better routes, smoother. And, yeah, it was nice."

Jamal said his former trainer, Tony Villani, made the whole thing possible ... explaining that whenever Jazz gets time off school, Villani's down to host him while other NFLers are getting their work in.

Jamal said at one point in his career, he was able to do for youngsters what Kelce did for his son ... and he called it all "a good thing."

"Later on," Jamal said, "they'll really cherish it."