Tyson probably came into his prime shortly before he challenged for the title and started to deteriorate after the Spinks fight. Even though that probably consisted of 3-4 years he amassed a record of 34-0. Lennox Lewis was a pro for over 9 years before he had a comparable number of fights so although it was a short time period it was far more active than most heavyweight champions.
Sad thing is,Tyson's prime could have lasted 2 - 3 years longer than it actually did. He lost all focus after the Spinks fight. It all went slowly downhill from there.
Pretty much the reason why he had so many fights in such a short time period. His handlers knew he would go off the rails as soon as he had time on his hands. Tyson basically fought took a week off and then went right back to the gym to get ready for another fight. Too bad it worked out the way it did because he was coming up on some pretty good fights with Bowe and Holyfield where we would have really seen what Tyson could do. Tyson was still fairly green himself even after winning the title but towards the Spinks fight he was really putting it together.