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Sean Penn is doing his best to keep up with much younger girlfriend Scarlett Johansson, and if daily jogs keep his body tight, keep on running!

Penn, 50, is enjoying accolades for his recent film Tree of Life ... co-starring Brad Pitt. The drama screened at the Cannes Film Festival ... and both audiences and critics praised the 2 1/2 hour flick. Kudos!

Now ... when is Mr. Penn going to star alongside his sexy younger lady, Scarlett? That would be sexy! See Mr. Penn looking buff in a white T-shirt ... after the jump.