A retired businessman enrolled in college for the first time — and joined the D-III football team as a freshman walk-on — after a dire cancer diagnosis reinvigorated his zeal for life. Tom Green, a 60-year-old Maryland native, stunned school officials when he tried out for the football team during his freshman year at McDaniel College. Now, he’s slated to be one of the oldest college athletes in US history, about a decade after beating cancer. When he was first diagnosed with stage four kidney cancer in 2015, Green said he was certifiably “dying.” “I was 60 pounds less, I…