The 53-year-old was coaxed into the cage by some of MLB's biggest superstars down in Miami as they were prepping for their WBC game against Venezuela on Saturday ... and he smashed bombs over the wall over and over again.

With his signature left-handed stroke, Griffey Jr. -- who's helping coach Team USA this year -- peppered the right field seats ... and check out some of the video of the scene, guys like Nolan Arenado were in awe!

In fact, almost the entire Team USA roster crowded around to get a glimpse of the legend's swings -- and each dude had a huge smile on his face with every pitch.

Of course, it probably shouldn't be too surprising, Griffey didn't retire that long ago -- 2010 ain't that far off -- and he did hit 630 dingers in his 2,671 career games.

Then again, 53 isn't exactly young for a baseball player!!

It's become a bit of a theme around Major League Baseball, though, because just last week, Aaron Boone uncorked a tater to deep left field on his 50th birthday.