Edge retired in 2011 for the same reason as Stone Cold: his neck. He was suffering numbness in his arms, was beginning to struggle through matches, and was told that one more neck injury could leave him paralysed. He, rightly, decided to retire then and there, his last match being successfully defending the World Heavyweight Championship at Wrestlemania 27. Although he had been on WWE TV since 1998, Edge was only really a main-event level guy for the last five years of his career, after winning his first WWE Championship in January 2006. So his retirement announcement came as a huge shock to the wrestling world, who still considered the thirteen year veteran a young talent. It was also a real shame as he left the WWE right before the beginning of their current "youth movement". He missed out on a feud with a fully-realised (read: fully bearded) Daniel Bryan. A Bryan vs Edge match series would have been incredible, no doubt. He missed out on getting attacked by The Shield, not to mention how much fun it would be to watch Edge and Dean Ambrose's personalities knock against each other. And he missed out on Bray Wyatt. And we missed out on Edge vs Bray Wyatt. We missed out on all of these.
Michael Palmer is a contributor at whatculture.com and thelineofbestfit.com, and he probably likes WWE slightly more than most people would call "healthy".
