#3 Physical limitations

Kane is 51 years of age, and a large majority of fans as well as pro-wrestling experts have for long been calling for The Big Red Machine to hang up the wrestling boots.
However, I strongly disagree that Kane's age has much to do behind him being better off stepping away from active in-ring competition. In fact, Kane is extremely fit and agile for a 51 year old man.
R-Truth wanted to 'kill' former WWE writer. More details HERE
Notwithstanding, it's the big man's future which seems truly worrisome. If Kane continues to tax his body by taking bumps after a career which has already spanned about 26 years, he'd quite likely have to deal with bone, joints as well as brain damage issues which several other pro-wrestlers have faced over the years...It's better to stop wrestling, than risk permanent damage just to prolong your career a little bit more...