... , I rarely see teachers work beyond 55, and yet they don't have a more physically difficult job than mine. 

So much so, Boudi, that I can think of many who carried on until 65 and, in all my years of teaching, I can only think of a handful who took early retirement at the age of 55.  Some at 60, yes; many, by actually being made redundant, through school amalgamations and creative accounting by LEAs who wanted to shed staff.  Sadly, many of the early retirees were the good teachers who knew that they could get good jobs elsewhere for the last few years of their working lives.