Deke Slayton was one of the seven mercury mission astronaut. He was supposed to be flying on the second orbit flight but couldn't because of a erratic heart rate. He was replaced by Scott carpenter( one of the seven mercury mission astronaut). He was lucky that he got one more chance to go to space at the age of 51 which was the record of being one of the oldest man to go to space but was beaten by John Young who went to space at the age of 53 and John Glenn who broke Young's record by going to space at the age of 77.  He then died at the age of 69 on June 13, 1993.