Installing cs5.5 in this day and age

Hello! I am a thrifty person who purchased CS5.5 Design Premium in 2011. I would like to carry over the use of my adobe products on my macbook air. As such, I promptly downloaded the appropriate file. An hour later, the time came to actually install the little stinker, and I hit a wall. My computer won't let me download it, presumably because it is so archaic at this point. Can someone help?