I had one for a little over a year. Ran out of algae so I gave it away.
Later bought another and had it for about a year and then gave it away.
Not sure of the life-span, but I think they are very sensitive to water chem. Try acclimating them well, the stress of a poor acclimation or a weak animal may cause an early death.
I have never had one die, but have never had one for more then about 14+ months either.