At age 11, Kyle Robidoux was diagnosed with a rare, degenerative eye disease called retinitis pigmentosa. While his vision has steadily gotten worse, he has learned to adapt to his impairment and sees no reason not to set new boundaries and test his physical limits. On Monday morning, Kyle, now 41, will rise well before dawn to lineup at the finish line of the Boston Marathon and run from Boylston Street to the starting line out in Hopkinton. After approximately an hour to regroup, he’ll set off with the rest of the marathon field (and his two sighted guides) to finish his “Boston Double."