"There aren’t a fixed number of jobs."
In the case of my mailman, there is. If he retires, another person is hired to take his route. This is the case with many jobs. Clearly I'm not speaking about ALL jobs, just as when I posted the comment about the students who didn't get a job after college that I wasn't talkin about students who got a degree in basket weaving as another posted suggested. I shouldn't have to explain that my comments are not meant to cover ALL situations.
"The existence of old people is not the cause of unemployment."
Perhaps you meant to post this under someone else's comment, because I didn't claim that the "existence" of old people was "the cause" of unemployment. However, if a 75 year old man retires, it opens up a job for anyone who is younger, be it a 20 year old person or a 55 year old person.