*In many countries the proportion..(there be no comma)
*In many countries all over the world, mainly western countries, the eldery make up....
*(Whenever using "and" to link 2 sentences, a comma is nessecary. check your essay)
* If these same people who retire live for,say,....
*....working with the same, when not better, qualifications ( it has no meaning or may be it lacks a verb. try to state it differently)
(Don't forget that one day you'll be old)
****PLEASE BE VERY CAREFUL WITH YOU PUNCTUATION*******
-----lOTS OF MISSED COMMAS-----