The year was 1968 and a young Harvard Freshman, Bennett “Ben” Hastings Beach, set off to run his first Boston Marathon. 50 years later, he’s still running this great race, without missing a start. Since 2002 the runs from Hopkinton to Boylston Street have become much more difficult. That’s when a muscle disorder, later diagnosed as Dystonia, began to affect his stride and slow his pace. Still, he ran the 121st Boston Marathon…