Dave McGillivray finished his first marathon at 18. He ran across the country at 23, then completed his first Ironman at 26. He has finished 46 Boston Marathons in a row, all while directing the race since 1988. Last January, he knocked off seven marathons on seven continents over the course of seven days in the World Marathon Challenge. At 64, there’s little in the endurance running world that he hasn’t achieved.