By Alek Arend Longtime Nationals first baseman Ryan Zimmerman has fielded his last grounder and taken his final swing. The 37-year-old announced his retirement on Tuesday afternoon. “When we first met I was a 20-year-old kid fresh out of the University of Virginia — the very first player ever selected by the newly created Washington Nationals in the 2005 draft. I had no idea how unbelievable the next 17 years of my life were going to be,” Zimmerman wrote. This was expected, but it’s still a bit hard to believe. Ryan Zimmerman was the heart and soul of the Washington Nationals for so many years…