What is a good target weight for 6 ft. 26 year old male?

Maybe 170 pounds: Varies with age and with muscle mass. Normal men are a wide variety of weights, but if looking for a simple number, just start with 106 pounds for 5 feet, and add 6 pounds for each inch over 5 feet (in this case, 106 + 72). Young men often start slimmer and lighter than 178 pounds at 6', but gain as the years go by, and tend to end up over 170 pounds some years later.