A day after celebrating his 40th birthday with a goal, Kawasaki Frontale stalwart Kengo Nakamura on Sunday announced he will retire at the end of the J-League season.The former Japan midfielder became the league's oldest-ever Player of the Year in 2016 at age 36. He helped Kawasaki win their first title in 2017 and go back-to-back the following year."I've been able to hang in for the past five years because I had already decided to retire (at 40). There wasn't a shadow of a doubt," Nakamura said during an online press conference.A member of the Samurai Blue squad that reached the last 16 at…READ FULL ARTICLE