Haha.... The above poster must still abide by the Weider Principles. Kiss your mass goodbye lol. Many multi sport athletes look better than "exclusive" body builders, clean or not.
To the OP.....If you have ever competed in a half or full marathon, can swim competitively, and can maintain 15-20 mph for an hour or so on a bike, then yes you can participate in an Ironman or Half Ironman.
Make sure you train to the point of minimal time acceptance, as there are cutoff times for each discipline. If you fail to make cutoff, your race is done and you trained only to be disappointed.