I think it's more depend on the keepers and tank size, diet and water condition. For me, they last around 18~24 months (2 different fish at 2 different time) and it was ate/act fine in the morning and died in the afternoon all of sudden.
*Tank size 72x24x24 and my Army around 16~18 inches, diet mainly on market shrimp and large lake smelt, tankmate is a RTC similar size.