I believe Rocky retired because he felt it was the right time for him. He wasn't a concerned about any opponent. He was so dedicated to boxing when he was fighting. He lived it. That along with possibly some resentment against Al Weil and those back problems. The way that Marciano fought he had to be 100% focused and in top shape or he would be beaten rather quickly. His style wasn't suited for longevity anyway.
once your back is cooked, you shouldnt be in boxing. it wont get much better either - you need to leave any kind of dangerous sport, you'll be afraid of being put in a wheelchair for life.
We had another thread on here a while back asking if Rocky decided to go 50-0, how would he do against Patterson. This is what I wrote, which I think is still valid for the question posed. "I'll throw another wrinkle out there just for the sport of it. There is no guarantee of course that Patterson would have been the chosen one for the magical 50-0. For one, he was still a light heavy at the end of the '55 ratings and just broached the division in early '56. Rocky last fought in September I believe and negotiations would have already started before the end of '55. But the top guys - I think - when Marciano retired in April of '56 would have been Bob Baker, Hurricane Jackson, Nino Valdez, Johnny Holman and probably Patterson just squeezing in there. I left out Moore because Rocky had just beaten him. Looking at it from Rocky's canny manager Al Weill's perspective, and wanting Rocky to go out with a bang, I would have stayed away from the speedy Patterson, the big guys like Valdez, Baker and Holman and gone for Hurricane Jackson. The perfect opponent. He had just nicked a highly controversial decision over Baker in early '56 (I think), he was small and wouldn't duck if his life depended on it. Ergo, the perfect opponent to see off Rocky. Again, just throwing a different angle on this."
Well this one has been debunked in classic ESB style. Rocky, like Lewis, got out at the EXACT right time. Neither felt it anymore. Three cheers for two absolutely perfect retirements. How often do we see the horror stories, slurred speech or even worse. I tip my hat to the great retirees such as Lewis, Marciano and the like. It's threadworthy!
Tyson was only 20 years old too and I think that Marciano's eyes would have been too big for his stomach if he thought he could take a 20 year old Tyson.