I foresee two possibilities. One, coming face to face with himself 17 years older would put him into shock and he’d simply pass out. Or two, the encounter could create a time paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space time continuum, and destroy the entire universe! Granted, that’s a worse case scenario. The destruction might in fact be very localized, limited to merely our own galaxy and Blake Griffin’s free throw shooting percentage.