In my opinion, and like I told you in the swordtail thread, it would take exactly 0 years.
Sorry, but I can't understand how anyone could exspect his problems to be solved by waiting till the fish die. Get them a bigger tank NOW, or find new homes for them.
AFAIK, platies and swordtails can live 2 to 5 years, plecos, other catfish and angelfish more than 10 years, and I think they all deserve a chance to reach their natural life span.
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Gisela
moppel@gismo.owl.de