What is the average lifetime of a typewriter?  Hmmm. Like anything else, it depends on what kind of maintenance the machine has had, how it's been used, how often it's been used, et cetera.  I have seen typewriters that have been destroyed after about five years.  But then I have seen (and own) typewriters well past one hundred years and still ready and rarin' to go.  I remember reading an article about a company that produced typewriters (they didn't reveal the brand).  An adsman asked the CEO how long their typewriters lasted, and he said:  "I don't know.  My secretary is still using the first one we ever made!!"