John Cena is reflecting on his momentous 20-year career in the WWE ... as he reveals his body is telling him it's time to move on.

Check out the clip -- the actor and professional wrestler appeared on "The Tonight Show Starring Jimmy Fallon" Wednesday and told the late night host he needs to retire so younger hopefuls can get their chance to shine just as he did back in the day. Gallery Launch Gallery Getty

John -- who admitted his body is yelling at him to hang it up -- explained to Jimmy he isn't trying to dwell on the past during his farewell tour. Instead, he says he's keeping his "feet on the ground" and soaking it all up as he moves into the 11 final matches of his ongoing tour.

He notes he'll have the chance to bask in the glow of his fruitful career once the tour is c

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