The existence of old people is not the cause of unemployment. On the other hand, enforcing the work week maximum of 48 hours, from the ILO convention in 1930(!), would actually help and doesn't need age discrimination.
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.
In my career I have seen retirement most often used as a way to downsize not to hire young people