I agree its between 2 and 4yrs, i have a 2yr+ old platy and she is thriving well so i know its at least 2yrs that they live for, genetics and care for the fish count alot though. If the fish is badly inbred, you would expect the fish to reach 2yrs max, but a healthy, reasonably well bred, well cared for platy should get to 4yrs. How many times the fish gets sick, what sort of enviroment it lives in and what other fish it is put with count alot though in getting to that 4yr mark.