Ken Griffey Jr.'s still got it ... The Kid stepped into the batter's box during Team USA World Baseball Classic BP on Friday -- and showed his sweet swing has not evaporated one bit with age!!!
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 .